CN1203828A - Catalyst for vecovering elemental sulphur selective oxidation of hydrogen sulfide and its preparing method - Google Patents

Abstract

The present invention relates to a catalyst for treating sulfur-bearing discharged gas. It can implement the selective oxidation of H2S to obtain element sulfur. Said invention is characterized by that in the course of preparation of the catalyst it uses inorganic acid, for example, phosphoric acid to make modification so as to make its surface do not produce activity on Claus reaction, and adopts the phosphate substances, such as ferric phosphate and chrome phosphate, etc. as catalytic activative substance to raise the activity and selectivity of sulfur production reaction.

Description

Selective oxidation of hydrogen sulfide recovery of elemental sulfur catalyst and preparation method

The invention relates to a sulfur-containing exhaust gas treatment catalyst and its preparation method, in particular, the present Invention relates to a method for selectively oxidizing hydrogen sulfide to elemental sulfur catalyst and catalyst Methods.

In the oil and gas processing, produce large amounts of hydrogen sulfide (H₂S) gases. In order to protect the ring Habitat and recovery of elemental sulfur, Claus process commonly used in industry deal with acid gas containing hydrogen sulfide.

Conventional Claus process sour gas feed to a third of H₂S In the high temperature combustion of oxygen furnace Of a SO₂，SO ₂And then with the remaining H₂S reaction of elemental sulfur: $H_{2}S+\frac{3}{2}{O}_2\→S{O}_2+H_{2}O$ $2H_{2}S+S{O}_2\→\frac{3}{n}\mathrm{Sn}+2H_{2}O$ To maximize the recovery of elemental sulfur, must be maintained H₂S∶SO ₂= 2:1. Moreover, since the reaction temperature is Degree of restriction of chemical equilibrium, even when the device is in good condition and operating conditions, the use of good activity Catalysts and three conversion processes, Claus sulfur recovery can only reach up to about 97%, The remaining H₂S, gaseous sulfur and sulfur which is equivalent to the amount of processing apparatus 3-4% sulfur, and finally to SO₂Form into the atmosphere, which seriously pollutes the environment.

H ₂S to elemental sulfur in direct oxidation reactions with H₂S and SO₂Phase Claus reaction carried out Instead, the following formula may be speaking from a thermodynamic reaction: $H_{2}S+\frac{1}{2}{O}_2\→\frac{1}{n}\mathrm{Sn}+H_{2}O--\left(1\right)$ In the absence of catalyst, the reaction (1) very slowly, and only at a temperature close to 300 ℃, Reaction is rather obvious, but when the reaction temperature exceeds 300 ℃, but also accelerated the generation SO₂Side effects: $H_{2}S+\frac{3}{2}{O}_2\→S{O}_2+H_{2}O--\left(2\right)$ $\frac{1}{n}\mathrm{Sn}+O_2\→S{O}_2--\left(3\right)$ $\frac{3}{n}\mathrm{Sn}+H_{2}O\→2H_{2}S+S{O}_2--\left(4\right)$ If the reaction temperature exceeds 400 ℃, generate SO may also occur₃Side effects:

These side effects will reduce H₂S direct oxidation of sulfur levels. H in industrial installations₂S Selective Catalytic Oxidation process conditions, mainly primary reaction (1) and the side reaction (2) to (4), can be expressed by the following formula: H ₂Oxidation of S can be considered as two parallel reactions (1) and (2), and the reaction (1) of the two subsequent reaction (3) and (4). The main reaction (1) to generate elemental sulfur is H₂S partial oxidation results, side reaction (2) to (4) to generate SO₂Is H₂S further oxidation results. In order to limit SO₂Generation, H₂S oxidation must be less than 300 ℃ the process conditions, and the reaction temperature should be higher than 180 ~ 190 ℃, in order to avoid the gaseous sulfur Condensation in the catalyst pores, so the development of a need to develop a high activity and selectivity of the catalyst, to promote Into the temperature range of 190 ~ 300 ℃ the H₂S selective oxidation reactions. Reaction (1) and (2) for the degree of The chemical composition depends on the catalyst, and the reaction (3) and (4) for the degree, in addition to the catalyst used The chemical composition, but also the pore structure of the catalyst, a large pore structure (low specific surface area) can Sulfur Once generated molecules will quickly leave the pores, avoid sulfur vapor according to the reaction (3) and (4) further oxidized SO₂。

According to U.S. Patent 4311683, BSR-Selectox process uses a carrier for non-alkali Porous refractory oxide of vanadium oxides and vanadium sulfide catalysts, and British Patent 2,122,597 intermediary Shao can be used Modop process uses a TiO₂Based catalysts. Lack of these two catalysts The process gas is to the high concentration of water content in certain limits, because Klaus paragraph Exhaust emissions after the hydrogenated with 25% to 30% water, a high partial pressure of water will drive the Claus reaction Balance in favor of generating H₂S and SO₂The direction, so the gas to the selective oxidation reaction The reactor is required before the contact condenser or quench water content in the gas stream is reduced to 5% (V) or so. Tail The water content in the gas is lower, H₂S conversion rate.

U.S. Patent 4,818,740 discloses a process from the high concentration of the catalytic effect of water content Agent, the catalyst can be used in Super Claus process, the carrier is α-Al₂O ₃, The active ingredient is Fe₂O ₃-Cr ₂O ₃. The catalyst composition of the gas to H₂S 1％(V)、O ₂ 0．6％(V)、H ₂O 30% (V), the balance helium and the reaction temperature 270 ℃, 1000h^-1Gas space velocity under laboratory conditions, H₂S conversion Rate of 100%, the selectivity of up to 93%. But industrial installations operating data has indicated that the upstream mining Claus catalytic conversion process with two selective oxidation reactor, the process gas at the inlet water content far Reached 30% (V) of more moderate conditions of an industrial atmosphere, H₂S is the actual conversion rate of 95 ~ 96%, the selectivity was 80 to 82%, the yield of sulfur which is only 76 ~ 79%. The catalyst in industrial conditions Selective is not high, indicating that it failed to maximize the suppression reaction (4), which may lead to the establishment failed to exclude The equilibrium Claus catalyst surface of the solid base. Furthermore, the catalyst preparation method is not Simple enough, the preparation of iron complexes of ammonia and ammonium chromium need to use a 25% solution of concentrated aqueous ammonia, the drying process will be Release of ammonia; while, in order to completely cover the active ingredient with the carrier containing alkaline or insignificant portion Position, the first active ingredient with a complex salt was impregnated α-Al₂O ₃Powder, dried, and then 160MPa Pressure extrusion molding, preparation process is more complicated.

Disclosed in European Patent 409353A1 catalyst preparation procedures and methods for their U.S. Patent 4818740 substantially the same, except that the high surface area carrier is a SiO₂Vector, not α-Al₂O ₃Load Body. The high activity of the catalyst surface area as small α-Al₂O ₃Based catalyst, but its activity at low temperatures, but Is obviously superior to α-Al₂O ₃Based catalysts. In industrial installations, the use of these two catalysts mixed square Method, the inlet temperature can bed 255 ℃ reduced from the original 200 ℃, at the same time, the maximum temperature bed Also dropped from the original 300 ℃ 260 ℃. Given the adiabatic condition, 1% (V), H₂S selective oxidation To elemental sulfur, the resulting reaction heat sufficient to reactor bed temperature 60 ℃, thus reducing bed Layer relaxes the inlet temperature means that H₂S concentration limits, H₂The concentration of S from the original 0.55% (V) ~ 0.65% (V) widened to 0.9% (V) ~ 1.0% (V), thus increasing the operation of the apparatus Be flexible and make the total sulfur recovery unit from 98.0% -98.3% to 98.7% ~ 98.9%. But according to the above-mentioned technical ideas, want to need to improve the overall sulfur recovery unit, the need to further improve the catalyst Activity levels.

The object of the present invention is to provide a preparation method is simple, the new high activity for H₂S selective oxidation catalyst Agent.

In preparing the present catalyst, in order to ensure that the reaction conditions in the gas phase catalyst exposed Surface is not alkaline, improve H₂S to elemental sulfur direct oxidation selectivity, the carrier used for preparing α- Al₂O ₃Should no alkali, or the amount of alkali metal and alkaline earth metal hydroxides of less than 3% (m / m), and the use of the acidic substance are inorganic acids such as phosphoric acid in particular to modulate the sub Claus reaction-inert non- Carrier and an alkaline catalyst surface, inhibiting the occurrence of side reactions Claus while using substances such as phosphates Phosphate, iron phosphate, chromium, supported on a carrier, as a catalyst active component.

As we all know, according to the Lewis acid-base theory proposed, Al₂O ₃Acid sites present on the surface and the base Hydrates chiral centers are generated during the dewatering process, this process can be roughly expressed as follows:

Wherein (a) said Lewis acid sites, electron-deficient central part, (b) said basic sites, is charged Sub-center. The roasting process and the degree of dehydration of alumina and alumina crystal relevant. After Above 1200 ℃ high temperature treated α-Al₂O ₃Generally regarded as chemically inert substances, in theory, should have Not contain or contain basic sites obvious, but in fact even pure α-Al₂O ₃Also due to dehydration Process will inevitably produce lattice defects, more or less always show some degree of acidity Nature, especially industrial α-Al₂O ₃Also often contains impurities, further strengthened its base properties. Such as alkali metal Or alkaline earth metal oxide impurities will increase the α-Al₂O ₃The alkaline nature of the halogen impurity ions are Enhanced α-Al₂O ₃Acidic nature. Increasing Al₂O ₃Alkaline, helps the Al₂O ₃Based catalysts Claus activity, but it is precisely the Claus reaction H₂S is oxidized to elemental sulfur directly inverse reaction, It should try to curb the Al₂O ₃Rendered alkaline; introducing F^-、Cl ^-Such as halogen ion, although increases Al₂O ₃Of Acid, but the high temperature firing device be serious corrosion.

Thus, the effective modulation Al₂O ₃Alkaline-based catalyst surface is to improve the H₂Direct oxidation of S The key element sulfur selective. In the present invention, by introducing an inorganic acid such as phosphoric acid, not only effectively modulation The α-Al₂O ₃Catalyst for the base, while the morphology of the active ingredient with the existing patent CN87103687 the different.

The present invention uses a temperature-programmed reduction (TPR) techniques and CO₂- Programmed desorption (TPD) The catalysts were characterized by technical research. As can be seen from the TPR results (see Figure 1): In industrial α- Al₂O ₃On, Cr₂O ₃Reduction of low chromium reduction peak temperature ratio Fe₂O ₃Reduced to cheap iron reduction peak temperature Clearly in advance, indicating Cr₂O ₃Than Fe₂O ₃Easy to H₂Reduced to low state; in FeCr / α-Al₂O ₃Appears on three samples of hydrogen consumption peaks, with Cr / α-Al₂O ₃And Fe / α-Al₂O ₃Compared to samples shows that the first consumption Hydrogen peak of Cr₂O ₃Reduction of hydrogen consumption peaks, the second and third reduction peaks of Fe₂O ₃Reduction of hydrogen consumption peaks, while in According to the present invention is prepared by adding phosphoric FeCrP / α-Al₂O ₃Sample, the TPR curve (Figure 1 a, b, c, d line) were significantly different from the FeCr / α-Al₂O ₃Sample, when the added amount of P is small, the consumption of chromium reduction Little change in the hydrogen peak, but the peak temperature of the iron reduction was after the shift, and with the increase of phosphorus content, the reduction of chromium Hydrogen consumption peaks gradually become obvious, while the iron was hot hydrogen consumption peaks gradually disappear, while the reduction of the sample peak shape Has evolved into a broad reduction peaks, indicating that the introduction of phosphate only modulation of the active ingredient and a carrier Interactions, but also changed the active ingredient is the chemical form of the carrier surface. The X-photoelectron Spectroscopy, infrared spectroscopy and X-ray diffraction analysis confirmed that the Fe and Cr on the surface morphology of phosphorus chemical Phosphoric acid, iron and chromium.

From the CO₂-TPD results (see Figure 2) can be seen: pure Fe₂O ₃There are two CO₂Take off With peaks, respectively, at 79 ℃ and 326 ℃ at the office, indicating Fe₂O ₃There are two desorption centers and α-Al₂O ₃Only a low-temperature CO₂Desorption peak; But according to the present invention is prepared, plus a sample of phosphoric acid has been mainly table Now the high-temperature CO₂Desorption (350 ℃ or so), which shows the introduction of phosphorus modulation, the surface characteristics of the catalyst Resistance, adding a small amount of phosphorus desorption of CO can cause hypothermia₂The surface of the basic sites disappear, and the high-temperature CO₂Desorption With the active phosphorus content increases, the desorption peak area gradually decreases as the phosphorus content of 1.27%, Has largely undetectable CO₂Desorption, indicating that the introduction of phosphorus modulation basicity of the catalyst, and And with the increase of phosphorus content, the surface of the catalyst gradually decrease basic sites.

In the present invention, the use of the carrier shall be no significant activity for the Claus reaction inert carrier, for example, To use an alkali or alkaline surface is not significant α-Al₂O ₃. If I choose to alkali-containing α-Al₂O ₃Its amount of alkali Alkali metal and alkaline earth metal oxides, the percentage should be less than 3 mass%, preferably less than 0.3%, and With an acidic substance such as phosphoric acid to be modulated, is not significant to the surface alkaline.

Modulation with phosphoric acid, the phosphoric acid is added in an amount of not only the nature of the carrier, but also with the use Activity Components of the nature and volume. The content of phosphorus element phosphorus, was 0.01% (m / m) ~ 10% (m / m).

When preparing the catalyst of the invention, can be directly used iron, chromium nitrate and phosphate complexes formulated Impregnating the α-Al₂O ₃The method is simple; addition, the introduction of not only changed phosphate of iron, chromium surface of the carrier The traditional chemical form, but also effectively modulating the basicity of the catalyst, its activity and selection Resistance than conventional catalysts are significantly improved, thereby further improving the overall sulfur recovery efficiency of the apparatus.

Figure 1 is a diagram of different samples TPR;

Figure 2 is a diagram of different samples TPD.

Example 1

The 12gFe (NO₃) ₃·9H ₂O and 1.3gCr (NO₃) ₃·9H ₂O was dissolved in a small amount of demineralized water Then adding 4gH₃P _O4, and then diluted with demineralized water to 60ml, formulated into a pale blue containing [Fe (HPO₄)] ₄ ⁺And Cr₂H ₂(HPO ₄) ₄The complex solution. The preparation of liquid impregnation 97.5gΦ3mm α-Al₂O ₃Crowded bar (one kind of soda lime sintering industrial production of high alkali content α-Al₂O ₃, The specific surface area To 2.99m²/ G), and then dried for 24 hours at room temperature, then at 120 ℃ and then dried for 4 hours, after Calcination at 500 ℃ for 6 hours to obtain a pale yellow finished catalyst A, a specific surface area of 5.1m measured²/ G, Iron phosphate 4.15% (m / m), chromium phosphate 0.47% (m / m).

Example 2

Preparation steps of Example 1, but the H₃PO ₄Join minus the 2g, the resulting complex solution Slightly darker color, finished catalyst B was yellow rice.

Example 3

Preparation steps of Example 1, but the H₃PO ₄Join minus is 1.35g, the resulting complex is dissolved Liquid darker finished catalyst C was khaki.

Example 4

Preparation steps of Example 1, but the H₃PO ₄Dosage further reduced to 0.35g, this time due to Complexation is not complete, formulated liquid color was blue, the finished catalyst D was drab.

Example 5

The catalyst prepared in the above embodiment broken into 20 mesh to 40 mesh particle size, the sample 10ml Φ18mm diameter into a stainless steel reactor, placed above a thick layer of quartz sand 4cm to To ensure uniform mixing of the reactants, the reactor inlet gas comprising H₂S 1％(V)，O ₂ 0．6％(V)，H ₂O 30% (V), the other is N₂. Small devices using a laboratory to evaluate the activity of the catalyst.

All tests are typically 270 ℃ and 2500h^-1High space velocity conditions. H₂S conversion rate ηH₂s%, selectivity S_s% S% and sulfur yield is calculated as follows:

The formula [H₂S] _Entering,And [SO₂] _Entering,Represents a reactive compound H artifacts₂S% (V) and SO₂% (V) concentration Degrees. Activity evaluation results are shown in the following table.

Catalyst	H 2S conversion rate %	Selective %	Sulfur yield %
A	100	96	96
B	100	94.8	94.8
C	99	94.6	93.7
D	83.6	92.3	77.2
CRS-31	78.2	80.2	62.7

As can be seen from the data in the table: The activity and selectivity of catalysts of the invention is obviously superior to industrial CRS-31TiO₂Catalyst, and accompanied by the increase of phosphoric acid, the final form of iron phosphate, phosphorus Chromium catalyst has excellent activity and selectivity.

Claims (7)

1. A method for the H₂S to elemental sulfur in a selective oxidation catalyst, characterized in that the catalyst preparation Process, with a mineral acid to modulate the basicity of the catalyst, so that in the Claus reaction under the reaction conditions Inert to the catalyst and the catalytic active material is phosphate.
2. 2, according to claim 1, wherein the catalyst is characterized in that the inorganic acid is phosphoric acid.
3. 3, according to claim 1, wherein the catalyst, characterized in that the catalytically active material is iron phosphate and / or Chromic phosphate.
4. 4, according to claim 3, wherein the catalyst characterized in that the iron phosphate, chromium phosphate content of 0.05% ~ 30% (m / m).
5. 5, according to claim 1, wherein the catalyst, characterized in that the carrier is not used in the α-alkali Al₂O ₃。
6. 6, according to claim 1, wherein the catalyst, characterized in that the alkali used in the carrier is α- Al₂O ₃。
7. As claimed in any of claims 1 to 6 wherein the catalyst is one of the preceding claim, characterized in that the catalyst The content of phosphorus (as elemental phosphorus) is 0.01% ~ 10% (m / m).

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