FR2836063A1 - Adsorbent useful for removing hydrogen sulfide from hydrocarbon and/or hydrogen gas streams comprises zeolite A exchanged with potassium cations - Google Patents

Abstract

Adsorbent comprising zeolite A 5-45 % exchanged with potassium cations is new. An Independent claim is also included for purification or separation of a gas mixture comprising hydrogen sulfide (H2S) and hydrocarbons and/or hydrogen by adsorbing H2S on the adsorbent described above.

Description

<Desc / Clms Page number 1>

The present invention relates to a zeolite A adsorbent exchanged from 5% to 45% by potassium cations and a process for purifying gas in its impurities
H2S using such an adsorbent.

 Gas containing the compound H2S is conventionally encountered in the gas industry, the refining industry and the coal processing industry. The H2S molecule is a component of natural gas and crude oil and its content varies greatly depending on the field of production.

 Other so-called "organic" sulfur compounds, such as mercaptans or thiophene derivatives, are present in large quantities in oil and gas and are found in almost all finished products of the refinery.

 One of the major challenges in refining is the reduction of the sulfur content of these products to meet environmental requirements or allow their subsequent processing in catalytic units, for example cracking or catalytic reforming, the catalysts of which would be poisoned by sulfur. .

 To do this, the different flows of the refinery undergo a hydrotreatment that allows the reduction of organic sulfur in H2S in dedicated units; these are hydrodesulfurization units or HDS.

 More generally, all refinery conversion units treating sulfur feedstocks generate effluents containing H2S. This is obviously the case of hydrotreatment units (HDT) or hydrocracking units (HDC) of naphtha, kerosene, vacuum distillate gas oil, oil or residue.

 This is also true for all non-hydrogenating conversion processes, such as catalytic cracking (FCC), coking, visbreaking.

 In order to get rid of H2S, the oxido-reduction by an oxygen-containing sulfur compound is commonly described, either by the Claus reaction process between SO 2 and H 2 S, as described in particular by DE-A-3 507 617 or GB-A- 2 202 546, or by oxidation of H2S with H2504, as described by WO-A-95/21790.

<Desc / Clms Page number 2>

Another possible way relates to the use of solid chemical reagents, such as ZnO as described by EP-A-260,798 or EP-A-2560741, doped spinels as described by US-A-5, 514,351 or US -A-4, 263,020, zeolites 5A, 3A, 4A or 13X as described by EP-A-211 560, US-A-4, 329,160 or DE-A-2643756, alumina, silica, activated carbon or clays as described in BE-A-798,334, JP-A-82,002
368, JP-A-52021275, iron powder as taught by JP-A-52028471, or also carbonate deposited on a refractory support, as taught by US-A-
3.996, 335.

It is also known to use absorbents in the liquid phase, as disclosed by
US-A-4, 293,531, CN-A-1113824 or WO 87/01961.

 Finally, another known route involves the reversible physical adsorption of H2S, as taught by US-A-6,783,606, JP-A-05 212 236, DE-A-1444447 or DE-A-2315113.

 To return to the previous example of refining, the solution, which is nowadays adopted industrially today to treat the H 2 S formed as a result of the hydrodesulfurization reactions, comprises three stages: the first stage consists in generating one or more gases containing H 2 S by simple liquid / vapor separation or by distillation, the second step consists in separating the H2S compound from the gaseous mixture formed of the H2, H2S compounds and light hydrocarbons by an amine wash, for example MDEA, MEA, DEA, etc.

 the third step consists in directing the recovered H2S compounds after regeneration of the amines to a Claus unit, to finally produce elemental sulfur.

 The present invention provides an alternative to the second stage of treatment, that is to say the separation of H2S from the other constituents of the different refinery gases; it is in addition to H2S, light hydrocarbons and hydrogen. These gases can be either effluents or flows internal to the units, such as recycling gases for example. In the latter case, the extraction of the H25 from the reaction section generally makes it possible to improve the performance of the process.

 The table below presents some examples of refinery gas compositions.

 The compositions of these gases are highly variable depending on the organic sulfur content of the feedstock, the intensity of the cracking achieved (creation of C15 + gases) and the pressure and temperature conditions at which the gas is produced.

 This great diversity of gaseous compositions that can be encountered on an industrial site further complicates the task of enabling effective removal of H2S, regardless of the exact composition of the gaseous mixture to be treated.

<Desc / Clms Page number 3>

Board

<Tb>
<tb> Recycling <SEP> Recycling
<tb> Type <SEP> of <SEP> GAz <SEP> or <SEP> Purge <SEP> to <SEP> or <SEP> purge <SEP> to <SEP> Effluent <SEP> Cut <SEP> Gas <SEP > Cup <SEP> C3 <SEP> Fuel <SEP> Gas
<tb> High <SEP> High <SEP> GAz <SEP> C2 <SEP> Acid
<tb> pressure <SEP> pressure
<tb> Origin <SEP> HDS <SEP> Hydro- <SEP> Coking <SEP> or <SEP> Gas <SEP> Plant <SEP> Gas <SEP> Plant <SEP> Network
<tb> Gas <SEP> Oil <SEP> cracking <SEP> Visbreaking <SEP> FCC <SEP> FCC <SEP> Refinery
<tb> Pressure, <SEP> bar <SEP> 30 <SEP> - <SEP> 50 <SEP> 120 <SEP> - <SEP> 170 <SEP> 4 <SEP> - <SEP> 8 <SEP> 4 <SEP> - <SEP> 8 <SEP> 25 <SEP> - <SEP> 35 <SEP> 4 <SEP> - <SEP> 8
<tb> Temperature <SEP> C <SEP> 30 <SEP> - <SEP> 60 <SEP> 30 <SEP> - <SEP> 60 <SEP> 30 <SEP> - <SEP> 60 <SEP> 30 <MS> - <SEP> 60 <SEP> 30 <SEP> - <SEP> 60 <SEP> 30 <SEP> - <SEP> 60
<tb> H2S, <SEP>% mol <SEP> 1 <SEP> - <SEP> 5 <SEP> 0.5 <SEP> - <SEP> 3 <SEP> 5 <SEP> - <SEP> 25 <SEP> 5 <SEP> - <SEP> 20 <SEP> 0.5 <SEP> - <SEP> 5 <SEP> 1 <SEP> - <SEP> 20
<tb> H2, <SEP> mole% <SEP> 60 <SEP> - <SEP> 95 <SEP> 80 <SEP> - <SEP> 95 <SEP> 5 <SEP> - <SEP> 10 <SEP> 10 <SEP> - <SEP> 30 <SEP> - <SEP> 20 <SEP> - <SEP> 50
<tb> C1, <SEP>% mol <SEP> 3 <SEP> - <SEP> 30 <SEP> 2 <SEP> - <SEP> 15 <SEP> 10 <SEP> - <SEP> 30 <SEP> 10 <SEP> - <SEP> 40 <SEP> - <SEP> 10 <SEP> - <SEP> 30
<tb> C2, <SEP>% mol <SEP> 0.5 <SEP> - <SEP> 15 <SEP> 0.5 <SEP> - <SEP> 10 <SEP> 10 <SEP> - <SEP> 30 <SEP> 5 <SEP> - <SEP> 20 <SEP><5<SEP> 10 <SEP> - <SEP> 30
<tb> C2 =, <SEP>% mol <SEP> - <SEP> - <SEP> 10 <SEP> - <SEP> 30 <SEP> 5 <SEP> - <SEP> 20 <SEP><5<SEP><10
<tb> C3, <SEP> mole% <SEP> 0.05 <SEP> - <SEP> 5 <SEP> 0.05 <SEP> - <SEP> 5 <SEP> 10 <SEP> - <SEP> 30 <SEP><<SEP> 10 <SEP> - <SEP> 20 <SEP><10
<tb> C3 =, <SEP>% mol <SEP> - <SEP> - <SEP> 10 <SEP> - <SEP> 30 <SEP><5<SEP> 75 <SEP> - <SEP> 90 <SEP ><10
<tb> C4, <SEP> mole% <SEP> 0.05 <SEP> - <SEP> 3 <SEP> 0.05 <SEP> - <SEP> 3 <SEP> 10 <SEP> - <SEP> 30 <SEP> - <SEP><5<SEP><5
<tb> C5 +, <SEP>% mol <SEP><0.1<SEP><0.2<SEP><5<SEP> - <SEP><5<SEP><1
<Tb>

Alternative adsorption processes have been investigated, for example zeolite adsorbent TSA methods or PSA methods on polar adsorbents, such as silica gel or alumina.

 However, the present adsorbents are not entirely satisfactory.

 Thus, with known zeolites, such as 5A, 13X or CaX, the adsorption affinity is so high that it is necessary to heat to desorb H2S, according to the TSA method. Such a method is acceptable only when the H2S content is low (ie <a few%), since then the desorption phase can be carried out at spaced intervals, but for contents exceeding the percent this method is no longer usable because of the regeneration interval which would be too short.

 Adsorbents such as activated alumina or silica have also been studied. In this case, the adsorption of H2S is quite suitable for a PSA process, but unfortunately, the selectivity towards C3 hydrocarbons is lower, or even less than 1 for C5.

 Hence, the problem is to be able to have an adsorbent having both a good H2S / hydrocarbon selectivity and a H2S isotherm of satisfactory characteristics so as to be able to effectively purify gaseous mixtures based on

<Desc / Clms Page number 4>

d'hydrogène, d'hydrocarbures et de H2S par élimination desdits composés H2S sur ledit adsorbant.

hydrogen, hydrocarbons and H2S by removing said H2S compounds on said adsorbent.

In other words, the object of the invention is to provide a PSA process based on an adsorbent having an excellent selectivity for H2S with respect to hydrocarbons and hydrogen, and which can be used in the PSA or PSA / TSA process of a way of being able to recover both pure H2S compounds and, moreover, hydrocarbons and hydrogen with an excellent yield, despite the large variations in the compositions of the gas to be treated which may occur.

The solution of the invention is then an adsorbent for the separation or purification of gas comprising a zeolite A exchanged from 5% to 45% by potassium cations.

Depending on the case, the adsorbent of the invention may comprise one or more of the following technical characteristics: the zeolite A is exchanged at least 10% with potassium cations, preferably at least 15% with potassium cations .

 the zeolite A is exchanged at most 40% by potassium cations, preferably at most 30% by potassium cations.

 it also contains residual sodium cations, preferably the sum of residual cations sodium represents less than 90% of the exchangeable cations, preferably less than 85% of the exchangeable cations.

 it has a pore size of 0.35 to 0.45 nm, preferably 0.36 to 0.42 nm.

 - It is in the form of spherical particles, ovoid, elliptical, extruded, monolithic honeycomb, lamellar or foam - the adsorbent particles have an average size of between 0.2 and 5.0 mm, preferably between 0.5 and 3.0 mm.

 it comprises a zeolitic phase and at least one binder representing less than 30% by weight of the total weight of the adsorbent.

 it furthermore contains metal cations chosen from the alkali metal cations of the Li, Na, K, Rb and Cs group, preferably Na and K.

 The invention also relates to a process for purifying or separating a gas mixture containing H2S, and at least one other hydrocarbon or hydrogen compound, in which at least a portion of the H2S molecules present in said gaseous mixture are adsorbed on at least an adsorbent according to the invention.

 Depending on the case, the process of the invention may comprise one or more of the following technical characteristics: the gaseous mixture contains from 0.001 to 80% of H 2 S, preferably from 1 to 30% by volume.

 the gas mixture comes from a processing unit within a refinery.

<Desc / Clms Page number 5>

the gas mixture comes from a hydrotreating, catalytic cracking, thermal conversion or catalytic reforming unit or from one of the fuel gas networks of the refinery.

the gaseous mixture contains saturated and / or unsaturated C1 to C8 hydrocarbons, in particular methane, ethane, ethylene, propane, propylene, butane, butenes and pentane.

it is chosen from the VSA or PSA processes.

the gaseous mixture is at a temperature of between 20 ° C. and 80 ° C., preferably between 30 ° and 60 ° C.

the adsorption pressure is between 0.5 bar and 70 bar, preferably between 4 bar and 8 bar or between 20 bar and 45 bar.

the desorption pressure is between 1 bar and 8 bar, preferably 1 bar and 2 bar.

the flow rate of the gas stream is between 1 and 106 Nm3 / h, preferably between
1000 and 100,000 Nm3 / h.

 it is used in at least one adsorber, preferably in at least two adsorbers operating alternately.

a gaseous mixture containing less than 0.5% of H 2 S compounds is recovered, preferably less than 0.05%
The invention will now be better understood thanks to the detailed description which follows.

 It has been discovered that it is possible to obtain an adsorbent effective for H2S / HC separation by exchanging NaA zeolite with potassium (K).

 When passing from zeolite NaA (pore size 4A) to zeolite KA (pore size 3A), the size of the gaseous molecules admitted into the pores increases from about 0.4 nm to 0.3 nm.

 The H2S molecule has a kinetic diameter of about 0.36 nm, while that of methane is at 0.38 nm. Thus, a type 4A zeolite adsorbs the two compounds while a type 3A zeolite adsorbs none.

 Thus, there is a Na / K exchange rate for a zeolite A such that the H2S isotherm becomes compatible with use in PSA, while the selectivity to hydrocarbons is high and due to the restriction. adsorption of these by molecular sieving effect to the access of the adsorption pores.

 Curve 1 shows the adsorption isotherm of H2S on a zeolite A exchanged at different potassium levels according to the invention.

 Curve 2 shows the evolution of the adsorption kinetics of H2S as a function of the potassium exchange rate.

<Desc / Clms Page number 6>

Curve 3 shows the adsorption isotherm of methane, the smallest of the hydrocarbons, and therefore the most difficult to separate, on the same zeolite A exchanged at different levels of potassium according to the invention.

The isothermal measurement can be carried out gravimetrically or volumetrically, it expresses the amount of gas adsorbed as a function of pressure, for a given temperature, here about 25 ° C., after activation of the product under vacuum (pressure less than 0. 1 mbar ) at 4000C overnight.

The zeolites exchanged are prepared in the following manner.

Starting from a NaA, also called 4A, from the trade and this zeolite is put in contact with an aqueous solution of a soluble salt of potassium (for example the chloride) at a concentration of about IN, at a temperature of between 400C and 90C, for at least one hour, preferably with gentle stirring.

The final exchange rate is adjusted by the volume of solution relative to the mass of zeolite, by the concentration, or by the number of successive exchanges, or a combination of the three.

 The exchange rate is measured by chemical analysis, such as ICP (Inductively Coupled Plasma). In the case where the product contains a binder, it is up to those skilled in the art to take it into account in the analysis. Industrial manufacturers know how to adjust the exchange rate of their own products and can therefore appeal to them.

 Figure 1 shows the adsorption isotherms of H2S on zeolites A exchanged at varying potassium levels. As can be seen, the adsorption capacity is high at low pressures for curves C1 to C5, corresponding respectively to potassium contents of 0%, 16%, 25%, 35% and 42.5%, while C6 curve (48% potassium) show degraded adsorption capacities. It follows from these curves that adsorption of H2S is still acceptable at an exchange rate of 42.5% in K but no longer allow this gas for 48% in K.

 FIG. 2 shows the adsorption kinetics, that is to say the amount of H2S adsorbed as a function of time, for a pressure of approximately 2 bars and at 25 C. It can be seen that the curves C1 to C4 present a satisfactory kinetics. Indeed, it is clear from these curves that the adsorption rate of H2S is still acceptable at an exchange rate of 35% in K but no longer let this gas at low speed for 42.5% in K.

 Figure 3 shows the adsorption isotherm of methane on the same zeolites.

It can be seen that only the curves C1 and C2 have satisfactory capacities. In other words, and surprisingly, the zeolites partially exchanged with potassium adsorb methane for an exchange rate of 16% but exclude it from 25%.

<Desc / Clms Page number 7>

In other words, the quantity of potassium cations to be introduced by ion exchange in zeolite A must be chosen carefully since above a value of approximately 45%, the adsorption can not take place because the gas molecules can not penetrate the pores, while below a minimum exchange value of about 15%, the separation is not done properly.

Another advantage of potassium exchange results from the fact that this cation is less polarizing than sodium.

A zeolite NaA (4A) then adsorbs the H2S compounds with great strength, resulting from the dipolar interaction between each molecule of H2S and the electric field generated by the sodium cation. The resulting isotherm is abrupt at low pressures, which hampers use in the PSA process because it makes it mandatory to perform the desorption phase at a lower pressure than would be desirable.

The polarizing power of a cation is expressed by the formula, where e is the charge of the electron, Z is the valence of the ion, and r is its radius.

However, the potassium cation being larger than the sodium cation (respectively 0. 133 nm and 0. 095 nm), its polarizing power is lower, and therefore the adsorption isotherm is less abrupt (see Figure 1), and more suitable for use in PSA process.

Claims (16)

claims  1. Adsorbent comprising a zeolite A exchanged from 5% to 45% by potassium cations. 2. Adsorbent according to claim 1, characterized in that the zeolite A is exchanged at least 10% by potassium cations, preferably at least 15% by potassium cations and / or the zeolite A is exchanged at most 40 % by potassium cations.  3. Adsorbent according to one of claims 1 or 2, characterized in that it also contains residual sodium cations, preferably the sum of residual cations sodium represents less than 90% of exchangeable cations, preferably less than 85% of exchangeable cations.  4. Adsorbent according to one of claims 1 to 3, characterized in that it has a pore size of 0.35 to 0.45 nm.  5. Adsorbent according to one of claims 1 to 4, characterized in that it is in the form of spherical particles, ovoid, elliptical, extruded monolithic honeycomb, lamellar or foam.  6. Adsorbent according to one of claims 1 to 5, characterized in that the adsorbent particles have an average size of between 0.2 and 5.0 mm, preferably between 0.5 and 3.0 mm.  7. Adsorbent according to one of claims 1 to 6, characterized in that it comprises a zeolitic phase and at least one binder representing less than 30% by weight of the total weight of the adsorbent.  8. Adsorbent according to one of claims 1 to 7, characterized in that it further contains metal cations selected from alkali metal cations of the group Li, Na, K, Rb and Cs, preferably Na and K.  9. A method for purifying or separating a gas mixture containing HzS, and at least one other hydrocarbon or hydrogen compound, in which at least a portion of the H2S molecules present in said gas mixture are adsorbed onto at least one adsorbent according to the invention. one of claims 1 to 8. <Desc / Clms Page number 9>

10. Process according to claim 9, characterized in that the gaseous mixture contains from 0.001 to 80% of H 2 S, preferably from 1 to 30% by volume. 11. Method according to one of claims 9 or 10, characterized in that the gas mixture is from a processing unit within a refinery. 12. Method according to one of claims 9 to 11, characterized in that the gas mixture is from a hydrotreating unit, catalytic cracking, thermal conversion or catalytic reforming or one of the fuel networks. gas from the refinery. 13. Method according to one of claims 9 to 12, characterized in that the gaseous mixture contains saturated and / or unsaturated C1 to C8 hydrocarbons, in particular methane, ethane, ethylene, propane, propylene, butane, butenes and pentane. . 14. Method according to one of claims 9 to 13, characterized in that it is selected from VSA or PSA methods. 15. Method according to one of claims 9 to 14, characterized in that: - the gaseous mixture is a temperature between 200C and 80 C, preferably between 30 and 60 C,

 the adsorption pressure is between 0.5 bar and 70 bar, preferably between 4 bar and 8 bar or between 20 bar and 45 bar, the desorption pressure is between 1 bar and 8 bar, preferably bar and 2 bar, the flow rate of the gaseous flow is between 1 and 106 Nm3 / h, preferably between 1000 and 100000 Nm3fh, and / or it is implemented in at least one adsorber, preferably in at least two adsorbers operating alternately. 16. Process according to one of Claims 9 to 15, characterized in that a gaseous mixture containing less than 0.5% of H 2 S compounds is recovered, preferably less than 0.05%.