CN1174517A - Zeolitic desulfurazation agents and their application to CO2 -containing gas treatment - Google Patents

Abstract

It is now possible to desulfurize gas having a non negligeable content of carbon dioxide by limiting the production of carbon oxisulfide to a very low level by treating said gas with adsorbants comprised of very small cristals of partially calcic zeolite A which are agglomerated by low iron clays with reduced acidity and basicity. Such clays may be obtained by phosphatation of montmorillonite, bentonite, attapulgite or kaolin.

Description

Zeolite desulfurizing agent and its content of CO2In gas treatment processes

The present invention relates to a process for the desulfurization of gaseous hydrocarbons and to a zeolite adsorbent for use in the desulfurization process. The invention can be used in the petroleum, gas, petrochemical industry and petroleum processing.

For the purification of sulfide-containing gases, the adsorbents widely used belong to the class of a-type and X-type molecular sieves. For example, as described in the soviet patent No. su753449, they have the advantage of having a good dynamic sulfur capacity, thereby achieving high purification rates. Nevertheless, when they are used with untreated, natural or structurally similar gases having the following composition:

C₁20 to 100% by volume

C₂0 to 20 percent

C₃0 to 25 percent

C₄0 to 5 percent

H₂S0.0001 to 0.15%

CO₂1 to 50% (preferably 1 to 15%)

Residual components, e.g. from N₂，H₂He composition, they react

Is catalytically active and a majority of H₂S is converted to carbonyl sulfide which does not remain on the adsorbent and is found in the purified gas.

More precisely, when the gas contains more than 1% by volume of CO₂E.g. 2%, and 0.1% H₂In the case of S, 65-70% exchange, 5A molecular sieves granulated with kaolin binders can yield about 140 to 220mg/m³COS (see french patent No.2,618,085). In order to actually show the phenomenon, the standard of the Russian soil is 35-40 mg/m³。

The object of the present invention is to solve these problems and to provide adsorbents having a high capacity for gas desulfurization and, at the same time, effective for removing H from the gas₂S and totally limits COS formationCatalytic activity; more specifically, the adsorbent has a dynamic adsorption capacity of about 2% by weight, but the amount of COS formation is still limited to 35mg/m³A maximum value.

This result can be obtained according to the invention with CaA zeolites, the crystallite size range of whichAbout 1-2 μm, has a calcium ion exchange rate of 76-90%, preferably 78-88%, and is granulated with a natural mineral binder such as bentonite, kaolinite, montmorillonite, attapulgite (attapulgite) or the like, the iron content of the binder being less than 0.5% (as Fe)₂O₃Expressed as NH at 150 ℃) and a phosphate concentration of 0-3.4% (expressed as added aluminium phosphate), and an acidity of less than 0.1 mmol/g (expressed as NH at 150 ℃)₃Expressed as adsorption) and basicity below 0.15 mmol/g (in SO at 150 ℃), is₂By adsorption of (c).

Secondary porosity is an important feature of the sorbent of the invention. So far, only diffusion in zeolite crystallites has been considered. The inventors have uncovered a significant benefit by taking permeability as an additional property, permeability being 1/D through the equation 1/Dgr ═ 1/D_z+1/dpor.sec, where Dgr, Dz and dpor.sec are the diffusion coefficients of the particles, crystallites and secondary pores, respectively. They demonstrate that by increasing the secondary pore volume and the overall permeability of the particles to the adsorbate, the contact time of the adsorbate and the adsorbent is reduced, while the adsorption capacity is increased, a new result which can be demonstrated by example 7 below. The secondary porosity of the agglomerates (agglomerates) is estimated by hexane adsorption (from 0.18 to 0.95P/Ps at 20 ℃) and is preferably in the range of 10 to 500 angstroms (10X 10) for pore radius^-10rice-500X 10^-10Rice) of 0.42 to 0.55cm³(ii) in terms of/g. The secondary porosity can be controlled by appropriate selection of the conditions for the preparation of the agglomerated product, i.e. parameters familiar to experts, such as choice of binder, moisture content of the slurry, pressure of the mixing shaft, cooking speed, due to the use of gas generating additives during the pyrolysis cooking, such as syrups, methylene blue or surfactants, such as nonylphenol oxyethylenated to 40OE, in amounts of about 0.5 to 2.5%.

Ca of the adsorbent according to the invention²⁺/Na⁺The cation concentration has a direct effect on the catalytic activity of these products. Na of zeolite component to reduce COS formation⁺The concentration must be less than 1.4 meq/g, corresponding to Ca²⁺/Na⁺The exchange rate was about 80%.

However, very small crystals lose structure due to fairly deep ion exchange, and at this stage they form new catalytic centers that promote COS formation. Thus if crystals are chosen that are limited only to sizes below 1 μm, the high exchange rates required by the present invention can be achieved without destroying the crystal structure and COS formation can be significantly reduced only when small crystals are used. Probably because, in this case, the CO is reduced₂Residence time in the crystallites. In this way, the crystallite function size is limited to 1-2 μm.

The clay contains both iron and aluminum oxides, which act as activators in the formation of COS. Due to the influence of temperature, Fe²⁺And Fe³⁺There is a strong tendency to transfer and exchange with alkali or alkaline earth cations in the solid. Thus, an adsorbent that is not active for COS formation begins to produce COS after several thermal regeneration cycles, particularly due to the formation or presence of water at high temperatures. The invention relates to aBy using only binders (Fe) containing small amounts of free iron₂O₃Content less than 0.5%) solves this problem. The present invention also demonstrates that the COS formation reaction occurs in a bronsted alkaline field. This r-Al₂O₃Has a certain acidity and basicity (acidity is NH)₃The adsorption of (A) is 1.4 to 1.8 mmol/g, and the basicity is SO₂The adsorption of (b) is 0.8 to 1 mmol/g). These authors suggest deactivation of the active sites in the clay by phosphating. The phosphorization operation is simple and can be realized by mixing clay with an aqueous solution containing orthophosphoric acid or metaphosphoric acid with proper concentration. The relationship between the activity of COS formation and the basicity of the clay is illustrated in example 6.

The invention also relates to the application of the adsorbents in purifying natural gas or similar structural gas with the specific components, wherein the method is carried out under the pressure of 0.1-10 MPa, the temperature of 0-50 ℃ and the linear speed of 0.01-0.2 m/s.

Examples

The following examples are provided to facilitate a better understanding of the present invention.

Example 1:

combined effect of crystal size and exchange Rate

In this example, the binder is Engelhardt ASP 200 kaolin, its Fe₂O₃The content is 0.5%, and its acidity is 0.32 mmol NH₃Per gram. The passivation was carried out by mixing in a mortar at a mixing ratio of 1 g phosphoric acid solution to 9 g kaolin, the phosphoric acid used being 0.94%, and aging the mixture in an oven at 65 ℃ for three hours. The capacity of carbonyl sulfide produced, measurable by the carbonyl sulfide formation constant k (COS), is equal to 6X 10^-6mole·kg^-1·s^-1·Pa^-1。

The size of the currently used industrial crystal is 1-10 mu m, and the exchange rate is quite low; the crystal prepared according to the invention has the size of 1-2 mu m, has higher exchange rate, and is blocked by 20 percent of adhesive; the constants k (COS) of the two crystals were compared at 10^-6mole·kg^-1·s^-1·Pa^-1And (4) showing.

Preparation according to the invention for the Crystal industry

The exchange rate is 72 percent and 77 percent

k(COS) 12.2 9.5

These results show that the rate of COS formation is reduced using the adsorbent prepared according to the present invention.

Example 2

In this example, COS formation constants of commercial crystals (1-10 μm) agglomerated with either passivated or unpassivated binders were compared. The results clearly show that the use of passivated binders gives better caking results.

For crystal industry

Whether the adhesive is passivated or not

The exchange rate is 72 percent and 72 percent

k(COS) 6.2 12.2

Example 3

An adsorbent was prepared by using crystals (1 to 10 μm) having an industrial size without performing passivation under the conditions of example 1. The cation exchange rate is varied within a range of 60.5 to 97%. According to their carbon oxysulfide constant k (COS) at 10^-6mole·kg^-1·s^-1·Pa^-1Indicating that the activity of the particle sample was estimated.

Sample A-0A-1A-2A-3A-4A-5

Exchange Rate (%) 60.57278879297

Constant k (COS) 19.612.28.07.414.616.7

These results show that: to ensure that the constant k (COS) does not exceed 10, the exchange rate in the adsorbent must be in the range of 76-90%. An exchange rate of 78 to 88% is a preferable range, and in this range, the constant is at most 8.

Example 4

A series of adsorbents with an exchange rate of 78% (exchange rate of sample a-2 in the previous example) were prepared, but according to general expert practice, the crystallite size could be varied by adjusting the spontaneous appearance of the seeds during gel maturation, or by controlling the number of seeds when they are placed. For example, in the B-2 procedure, the composition is 2Na by ripening at room temperature₂O-Al₂O₃-2SiO₂-90H₂And (3) gelling the gel for 20 hours, and then crystallizing the gel for three hours at 100 ℃ to obtain crystals with the size of 1-2 mu m. The same procedure produces a narrow size gradient distribution due to the formation of a large number of seeds during the maturation period. Likewise, the B-4 working crystal also consists of a crystal having the same composition: 2Na₂O-Al₂O₃-2SiO₂-90H₂O gel, but it is seeded with enough seeds (finely ground zeolite 4A) before crystallization so that the final crystal size ranges from 3 to 4 μm.

The results are reported in the table below. As before, the carbon oxysulfide constant k (COS) is 10^-6mole·kg^-1·s^-1·Pa^-1And (4) showing.

Sample A-2B-0B-2B-3B-4B-5

Size (mum) 1-100-21-22-43-44-6

Constant k (COS) 8.012.23.18.68.421.9

These results indicate that a narrow distribution and smaller crystallites are preferred, with an optimum size of 1-2 μm.

Example 5

A series of adsorbents were prepared as in example sample B-2 above by granulating zeolite powders using kaolin-containing clays from different CEI deposits and having different iron contents. The amount of clay added was 20%. The results are given in the table below, which illustrates the presence of Fe in clay²⁺And Fe³⁺Iron is present in a weight percent concentration (in Fe)₂O₃% form) and the carbonyl sulfide constant k (COS) at 10^-6mole·kg^-1·s^-1·Pa^-1Representation).

Sample C-0C-1C-2C-3

Fe in clay₂O₃％ 0.1 0.44 1.2 3.9

Constant k (COS) 2.63.210.233.0

Example 6

In this test, the variable factor is the Bronsted pH of the binder in the adsorbent. For this purpose, the series of samples D-1 to D-3 was prepared as sample C-1 in the preceding example. The adhesive is gamma-Al with different pH values₂O₃Or η -Al₂O₃Final product ofSample 5% by weight was added to these samples. By NH₃Acidity by adsorption at 150 ℃ by SO₂The alkalinity was measured by adsorption at the same temperature and these values were measured using a mibeun scale. Therefore, the sample was first heated to 400 ℃ to constant weight in vacuum. NH (NH)₃Or SO₂The adsorption of (a) is carried out at room temperature under a pressure of 5 to 10mm of mercury (0.6 to 1.3 kPa). The excess adsorbate is then discharged. The sample thus treated was then heated to 150 ℃ for 1 hour under vacuum. Recorded NH for weight loss₃Or SO₂Expressed as milligram molecules per gram of adsorbate, to measure the ph. The results are shown in the following table.

Sample C-1D-1D-2D-3

Acidity NH₃(mmole/g)0.35 0.11 0.46 1.1

Alkalinity SO₂(mmole/g)0.28 0.08 0.15 0.78

Constant k (COS) 3.21.82.955.0

Example 7

In a laboratory apparatus with an adsorber diameter of 50mm and an adsorption bed height of about 3m, 5 kg of different samples are added each time. The incoming natural gas contains 2% CO₂1.1% ethane, 0.03% propane and 0.08% H₂S, and the balance being methane. The dew point at normal pressure is-55 ℃. Flow rate of 18m³H; pressure 55 bar, temperature 40 ℃. For this experiment, the following samples were prepared in bulk:

a-2 sample similar to example 3;

a sample of B-2 similar to example 4;

a sample of C-1 similar to example 5;

samples E-1, E-2 and E-3, with different secondary porosities, as illustrated in example 1, were made with crystals exchanged by 88% and with passivated binder, with different pore volumes obtained by adding different amounts of syrup or methylene blue solution as pore former to the binder.

A control experiment was carried out with sample A, which was prepared according to the prior art (French patent No.2,277,798).

For COS and H in effluent gas₂And (5) detecting the characteristics of the S concentration.

The results are as follows: sample A A-2B-2C-1E-1E-2E-3 crystals (. mu.m) 1-101-21-21-21-2 exchange (%) 72787878888888 Fe₂O₃% 0.810.810.810.440.440.50.5 alkalinity (mmole/g) 0.210.210.210.280.090.110.11 porosity (cm)³/g) 0.26 0.26 0.36 0.41 0.55 0.49 0.44H₂S Capacity (%) 2.21.82.352.33.12.82.7 COS flow-out (mg/m)³)215 175 165 58 18 26 30

These results further confirm that in H₂S adsorption capacity, the correlation of the selection of adsorbent parameters and the reduction in the outgoing COS ratio.

Claims (6)

1. For natural gas and with more than 1% CO₂The synthetic CaA zeolite-based adsorbent having a similar structure for gas desulfurization of (a) comprises:

75 to 85% by weight of zeolite A having a pore size of 1 to 2 μm and Ca²⁺The exchange rate is 76-90%, preferably 78-88%; and

-25% to 15% by weight of iron (as Fe)₂O₃Expressed) less than 0.5% by weight of clay, its acidity, with NH adsorbable at 150 ℃₃Expressed as less than 0.1 mmol/g, its basicity, with SO adsorbable at 150 deg.C₂Expressed as less than 0.15 mmol/g.

2. The adsorbent of claim 1 wherein the secondary pores are 0.42 to 0.55cm³Per gram of particles.

3. The adsorbent of claim 1, wherein the radius of the secondary pores is 10 to 500A (10 x 10)^-10m～500×10^-10m)。

4. The adsorbents of claims 1, 2 and 3, wherein the binder is a natural clay derived from montmorillonite, bentonite, attapulgite and kaolin treated with phosphoric acid to achieve an aluminum phosphate concentration of 0.2 to 3% by weight.

5. Use of the adsorbents according to claims 1, 2, 3 and 4 in a process for desulfurizing natural gas or structurally similar gases having a composition,

C₁20 to 100% by volume

C₂0～20％

C₃0～25％

C₄0～5％

H₂S 0.0001～0.15％

CO₂1-50% (preferably 1-15%) of a remainder, e.g. N₂，H₂And He composition.

6. Use of the adsorbent of claim 5 for the purification of a gas under the following conditions:

-pressure: 0.1 to 10MPa

-temperature: 0 to 50 DEG C

-linear velocity: 0.01 to 0.2 m/s.