Process for removal of mercury or arsenic from a fluid in presence of a recovery mass of mercury and/or arsenic.

The present invention relates to a process for removing, in a gaseous or liquid fluid, at least one metal or metal compound chosen from the group consisting of mercury and arsenic, by bringing said fluid into contact with a mass of capture of mercury and / or arsenic. This solid mass for capturing mercury and / or arsenic contains a solid mineral carrier or dispersant, copper and sulfur combined at least in part in the form of copper sulphide and in particular for example in the form of at least one Cu sulphide_xS_y (where x and y are each an integer from 1 to 10).

The solid masses of the present invention can be called indifferently: absorption, capture, extraction or trapping masses.

US-A-4094777 describes a process for the preparation of a mass for the capture of mercury comprising the incorporation of a copper compound into an inorganic support, followed by sulphurization at a temperature below 300 ° C.

Sulfurization according to the process described in this patent is carried out using a gaseous agent, for example hydrogen sulfide, or a solution of an inorganic sulfide in water or in an organic solvent, by example an aqueous solution of sodium sulfide, potassium sulfide or ammonium sulfide.

The masses obtained have a high activity and are relatively inexpensive. However, the preparation of these capture masses has several significant drawbacks.

Thus, when the sulfurization is carried out using gaseous hydrogen sulphide (H₂S), obtaining a capture mass, having sufficient activity usually requires working at high temperatures, for example of the order of 200 ° C, which is very disadvantageous. In addition H₂S is a toxic and smelly product.

The use of sulfide solution, for example aqueous ammonium sulfide solution, makes it possible to work at a relatively low temperature, for example between zero and one hundred degrees Celsius. However, ammonium sulfide is a toxic and easily decomposable compound, which complicates its use.

The use of other sulfides (sodium ...) brings additional cations into the mass, which is disadvantageous.

According to patent application EP-A-107582, a mercury capture mass is prepared by impregnating a support using an organic sulfur solution decomposable into elemental sulfur at a temperature below 150 ° C.

After drying and volatilization of the organic compound, or after the above decomposition, a support is obtained with a dispersion of sulfur in the unmelted free state.

US Pat. No. 4,474,896 describes a mercury capture mass obtained by bringing a support impregnated with a metal cation capable of forming an insoluble polysulfide with a mixture of sulfide and polysulfide.

In the tests described, CaCl₂ supports treated with elemental sulfur were prepared. Results obtained in the treatment of fluids charged with mercury are bad: there are too large quantities of mercury in the effluents.

It has now been discovered by the applicant that it is possible to capture mercury and / or arsenic from a gas with a solid mass based on copper sulfide, having good efficiency, and an improved lifetime and a lower manufacturing cost, said mass being obtained by treatment of a support loaded with copper oxide with elemental sulfur then activation.

More precisely, the process for removing mercury or arsenic is characterized in that the solid mass for capturing mercury and / or arsenic comprises the following steps:<ul id="ul0001" list-style="none"><li>a / at least one copper compound, other than a sulphide, is incorporated into a solid mineral support or dispersant,</li><li>b / in the event that said compound is not a copper oxide, the product obtained in step (a) is calcined so as to transform at least partially the copper compound or compounds which it contains into copper, (CuO and / or Cu₂O),</li><li>c / the product obtained in step (b), or in step (a) if there has been no step (b), is brought into contact with elemental sulfur,</li><li>d / the product obtained in step (c) is subjected to a heat treatment in a non-oxidizing atmosphere, with gas sweeping, at a temperature and for a time sufficient to allow the formation of sulfide of the metal or metals present.</li></ul>

The solid mineral carriers or dispersants are usually chosen from the group formed by carbon, activated carbon, coke, silica, silicon carbide, silica gel, synthetic or natural silicates, clays, diatomaceous earths , fuller's earth, kaolin, bauxite, refractory inorganic oxides such as, for example, alumina, titanium oxide, zirconia, magnesia, silica-aluminas, silica-magnesia and silica-zirconia , alumina-boron oxide mixtures, aluminates, silico-aluminates, crystalline or synthetic zeolitic alumino-silicates, for example mordenites, faujasites, offretites, erionites, ferrierites, zeolites ZSM5 and ZSM11, mazzites, and cements such as for example those of the Secar type produced by the company Lafarge.

Use is preferably made of a support chosen from the group formed by carbon, activated carbon, coke, silica, aluminas, silica-aluminas, silicates, aluminates and silico-aluminates (zeolitics for example).

Advantageously, the support is chosen from the group formed by silica, aluminas, silica-aluminas, silicates, aluminates and silico-aluminates and alumina is very advantageously used.

When the mercury and / or arsenic capture masses are intended to be used in the treatment of charges containing condensable hydrocarbons (for example C4 or higher than C4) at a temperature situated in the temperature range at which is carried out the capture, it was found that the masses having an average pore diameter at least equal to 100 Angstroms (10⁻⁸m) have increased stability.

The conditions for obtaining masses (or supports intended for manufacturing these masses) having an average pore diameter of at least 100 Angstroms (10⁻⁸m) are sufficiently well known to those skilled in the art not to be repeated here , in the context of the present invention (see for example US-A-4094777).

The preferred supports usually have a specific surface of approximately 20 to 300 m² xg⁻¹, these values ​​not being limiting.

The incorporation of a copper compound, other than a sulphide, into a solid mineral support or dispersant can be carried out by any method known to those skilled in the art, for example by mixing with a copper compound or by impregnation with using a solution of a copper compound. The commonly used copper compounds are compounds which can be easily transformed into copper oxide at relatively low temperatures.

As an example of a copper compound, there may be mentioned, without implying any limitation: copper oxides; copper hydroxide Cu (OH) ₂; basic copper salts, in particular carbonates of the formulas CuCO₃, Cu (OH) ₂ and 2CuCO₃, Cu (OH) ₂; the salts and organic complexes of copper such as the salts of carboxylic acids, for example formates, acetates, tartrates, citrates, benzoates, oxalates, malonates, succinates, glycolates, lactates and acetylacetonate and copper nitrate.

It is usually preferred to introduce the copper compound by impregnating the support using an aqueous or organic solution of a copper compound and preferably using an aqueous solution of a copper compound. Advantageously, an aqueous solution of copper nitrate is used.

A small proportion of a soluble silver compound can optionally be introduced onto the support. The amount of silver introduced into the support expressed in weight of silver relative to the support usually represents from 0 to 5% by weight. Other metals may also be optionally present, for example iron.

The solid mineral support or dispersant comprising a copper compound, other than a sulphide, is then optionally calcined so as to transform, at least in part, the copper compound into copper oxide. When, in step (a) of introducing a copper compound, a copper oxide has been mixed, for example, with the solid mineral support or dispersant, this calcination step is not necessary.

During this calcination step, the operating conditions are preferably chosen so as to transform at least most of it, that is to say at least 50%, and preferably at least 80% and very advantageously 100% of the copper compound present in copper oxide (CuO). The Applicant has in fact found that copper is particularly well fixed in the form of copper oxide. Calcination can be carried out in a neutral or oxidizing atmosphere. It is thus possible to operate in the presence of an inert gas such as nitrogen, argon, helium or a mixture of these gases. It is also possible to operate in the presence of a mixture of oxygen and inert gas containing for example from 1 to 60% by weight of oxygen or even in the presence of substantially pure oxygen.

The calcination is preferably carried out in an oxidizing atmosphere and air is advantageously used, but it is also possible to use air enriched with oxygen.

The calcination temperature is usually about 200 to about 1000 ° C and preferably about 300 to about 800 ° C and preferably about 350 to about 600 ° C.

The calcination can be carried out in a static atmosphere or under a stream of gas. It is usually preferred to operate under a gas stream, and an air stream is advantageously used. The hourly space velocity (VVH) expressed in volume of gas per volume of capture mass and per hour is usually about 100 to about 20,000 h⁻¹ and preferably about 100 to 10,000 h⁻¹ and often about 300 to 5000 h⁻¹.

The duration of this calcination step is usually from about 0.5 hour to about 24 hours and preferably from about 0.5 hour to about 12 hours and preferably from about 1 hour to about 10 hours.

The product usually containing copper oxide from stage (a) or from stage (b) of calcination is then placed in the presence of elemental sulfur, at least partly in the form of an organic solution or alternatively in the form of solid sulfur or also in vapor form, the sulfur condensing on the support during the heat treatment; the product resulting from this incorporation (step (c)) constitutes the precursor of the mercury capture mass of the present invention.

As organic sulfur solution, it is possible in particular to use sulfur particles in the native state or in flower whose average diameter is for example less than 20 microns and preferably between 0.01 and 10 microns in solution at least. partly and possibly also in suspension in an organic compound whose boiling point is less than 250 ° C such as for example: toluene, benzene, methyl alcohol, acetone, carbon sulfide or any other organic compound known to the skilled person where the sulfur is soluble and for example, a light gasoline boiling between about 60 and 95 ° C, a hexane type gasoline boiling between about 63 and 68 ° C, a gasoline of type F boiling between approximately 100 and 160 ° C (and containing in volume 10 to 20% of aromatic hydrocarbons) and a gasoline of the type "White Spirit" boiling between approximately 150 and 250 ° C (and containing in volume 14 to 22% aromatic hydrocarbons).

The support is impregnated with said organic solution, the total amount of sulfur being introduced in one, or possibly several impregnation operations with intermediate drying at a temperature below 150 ° C. It is necessary to carry out this or these impregnation (s) while avoiding the premature crystallization of the sulfur on the support due in particular to a too great temperature difference between the support and the organic impregnation solution. To achieve this objective, it may prove advantageous to heat the support beforehand to the same temperature as the impregnation solution.

The objective being to transform the copper oxide at least partly into copper sulphide, therefore to reduce the elemental sulfur to S⁻⁻, it was also discovered that this objective can be improved by adding to said solution at least one compound reducing agent chosen for example from the group formed by hydrogen, formaldehyde, acetaldehyde, formic acid, hydrazine etc.

The quantity of sulfur which is incorporated into the absorption mass is suitably chosen to subsequently allow the transformation of the copper compounds contained in said mass at least in part into copper sulphide. The amount of sulfur can easily be adjusted according to the amount and the stoichiometry of copper sulfide which it is desired to obtain.

It is usually desirable to transform all of the copper compounds present in the absorption mass into copper sulfide and therefore to use a quantity of sulfur calculated in sulfur atoms, at least stoichiometric, relative to copper, or to l 'copper and other metals present, in particular silver, calculated in metal atoms and this, for their highest stable valency, for example Cu²⁺, Fe³⁺, Ag⁺.

The amount of sulfur used, calculated in atoms, is advantageously such that the sulfur atomic ratio on active metals present in the mass is approximately 0.8: 1 to 2: 1 and preferably approximately 0.9: 1 to 1 , 7: 1. By active metals is meant those which capture mercury and / or arsenic, for example copper, silver, iron, etc. It is possible to introduce, for example, silver onto said mass, by incorporating a silver compound during step (a) of the process.

The precursor resulting from step (c) described above is then subjected in a step (d), called activation, to a heat treatment in a non-oxidizing atmosphere, for example neutral or reducing and preferably neutral, under scanning. of gas, at a temperature and for a time sufficient to allow the formation of sulphide of the metal or metals present.

This heat treatment is usually carried out under a stream of inert gas, for example nitrogen, argon, helium, or a mixture of two or more of these gases, or alternatively water vapor in a proportion less than 10 % vol preferentially less than 5% vol and very preferentially less than 1% volume. It is possible to add to said gas, 1 to 5% (volume) of a reducing compound chosen for example from the group formed by hydrogen, formaldehyde, acetaldehyde, formic acid, hydrogen, etc. When water vapor is present, it may be advantageous to add hydrogen for example, with a H₂ / H₂O ratio greater than 0.1% (volume).

In a preferred embodiment of this treatment, the absorption mass containing the sulfur and the copper oxide is treated under a stream of inert gas, at a temperature of approximately 100 to approximately 250 ° C., preferably approximately 120 at 230 ° C and often around 130 to 220 ° C, with an hourly space velocity (VVH) expressed in volume of gas per volume of capture mass and per hour of about 100 to 10,000 h⁻¹, preferably d '' about 300 to 5000 h⁻¹ and often about 500 to 2000 h⁻¹. The duration of this gas sweeping treatment is usually from about 1/2 hour to about 24 hours and preferably from about 1/2 hour to about 10 hours, with a duration of about 2 hours usually being sufficient.

During the heat treatment, there is a chemical interaction between the copper oxide, possibly promoted by Ag, Fe, and sulfur. We observe that there is release of SO₂ according to a possible reaction:<maths id="math0001" num=""><math display="block"><mrow><mtext>2 CuO + 3 S → 2 CuS + SO₂</mtext></mrow></math><img file="EP0484234A2_D0001.tif" /></maths>

When at least one reducing agent has been added with the sulfur during step (c), the proportion of sulfur eliminated in the form of SO₂ can preferably be reduced, as follows: <maths id="math0002" num=""><math display="block"><mrow><mtext>CuO + HCHO + S → CuS + HCOOH</mtext></mrow></math><img file="EP0484234A2_D0002.tif" /></maths>   or : <maths id="math0003" num=""><math display="block"><mrow><mtext>CuO + HCOOH + S → CuS + CO₂ + H₂O</mtext></mrow></math><img file="EP0484234A2_D0003.tif" /></maths>

After the heat treatment (step d), under gas sweeping, the absorption mass can optionally be dried, preferably under a stream of inert gas, for example under a stream of nitrogen, helium, argon or a mixture of two or more of these gases (in the presence or absence of a reducing compound such as that previously described) then optionally cooled to room temperature preferably in the presence of the above-mentioned gas stream, before being brought into contact with the fluid to be purified.

In another embodiment, which does not constitute a preferred embodiment, it is finally possible to insert a step (b ′) of reducing treatment at the end of step (b), in the case where the copper has been deposited by impregnation, or again at the end of step (a) if a copper oxide has been added by wet mixing with a support (no calcination).

The reducing treatment then aims to transform the copper oxide, possibly promoted by silver or even by iron, into metallic copper. Any industrial process known to those skilled in the art can be used, for example reduction in the presence of a gas containing hydrogen or else reduction in the presence of a reducing chemical compound such as for example aldehydes (for example example formaldehyde, acetaldehyde), hydrogen, (formic acid), as indicated above in improvement of step (c).

After reduction of at least 50%, preferably 70% and very preferentially 85% of the copper oxide to copper metal, as well as possibly the silver metal, (the iron if this one is present, being only partially reduced), the product obtained is brought into contact with elemental sulfur, for example optionally at least in part in the form of an organic solution or without solvent (step (c)), then is dried and activated according to step (d).

During this stage, the sulphide then forms stoichiometrically for the metallic copper fraction: <maths id="math0004" num=""><math display="block"><mrow><mtext>Cu + S → CuS</mtext></mrow></math><img file="EP0484234A2_D0004.tif" /></maths>

And as above for the copper fraction in the form of oxide: <maths id="math0005" num=""><math display="block"><mrow><mtext>2 CuO + 3 S → 2 CuS + SO₂</mtext></mrow></math><img file="EP0484234A2_D0005.tif" /></maths>

The capture mass obtained at the end of step (d) contains 8 to 25% (by weight) of copper sulphide, preferably about 10 to 20%, and in an often advantageous form 12 to 18% . Masses are usually preferred, at least 60% and preferably at least 80% of the copper (weight) being in the sulphide state.

Structural analysis shows that the sulfide is at least partly in the form of CuS and generally most of the sulfide is in this form. Other sulfides may be present, which have the formula CxSy where x, y represent an integer between 1 and 10.

The mercury and / or arsenic capture masses obtained are used to purify gases or liquids containing mercury and / or arsenic, for example gas condensates. These solid masses are usually used in the form of a fixed bed through which the fluid to be purified is passed.

The temperature range where the capture masses are effective is usually between approximately minus 50 ° C and plus 200 ° C. The capture of mercury and / or arsenic can be carried out at atmospheric pressure or under a lower or higher pressure, the total pressure possibly reaching for example 10 MPa. VVH for gaseous charges (charge volume per volume of capture mass and per hour) is usually around 500 to 50,000 h⁻¹, but one preferably operates at a VVH of around 2000 to 20,000 h⁻¹ and advantageously d '' about 4000 to 15000 h⁻¹; for liquid loads the VVH will preferably be approximately 0.1 to 20 h⁻¹.

The fluids treated using the capture masses prepared as described above, can contain for example from 10 nanograms to 2 grams of mercury or more, per cubic meter. The gases treated are most often hydrocarbons or mixtures of hydrocarbons such as, for example, natural gases containing a major proportion of methane and a minor proportion of C₂ and / or higher hydrocarbons and mercury. The treated gases often contain gases other than hydrocarbons such as CO₂, water and H₂S, in variable quantities.

The treated gas can also be hydrogen, such as for example electrolytic hydrogen; it can also be air provided that it operates under conditions of temperature and / or pressure such that contact with the gas does not cause the oxidation of the absorption mass or of an excessive part of said mass. It is also possible to envisage the treatment of mixtures containing several of the compounds or gases mentioned above.

The liquids treated are most often mixtures of hydrocarbons usually containing a major proportion of saturated hydrocarbons having from 4 to 50 carbon atoms in their molecule, for example gas condensates, having mercury and / or arsenic.

All the devices known to those skilled in the art, and commonly used for purifying fluids can be used. The mercury removal device can for example consist of a single reactor or of at least two reactors in parallel, but at least two reactors are preferably used in series.

If we consider the case of three reactors in series A, B, C, we preferably operate as follows: when the first reactor A has reached a capture efficiency which will be for example only 90% or 70% of its initial efficiency, regeneration or replacement of the capture mass contained in A. During the time necessary for this regeneration or replacement stage, the fluid will pass through reactors B and C; after the regeneration or replacement of A, the fluid will pass into B and C then into A; B will then be regenerated or replaced when its efficiency is no more than, for example, 90% or 70% of its initial efficiency; during this time the fluid will pass on C and A. After the regeneration or the replacement of B the fluid passes in C, A then B. We will then regenerate or replace C and so on.

The regeneration can be done either in the reactor, or in a unit provided for this purpose after unloading of the capture mass.

The regeneration is carried out by heating under conditions making it possible to remove the mercury and / or arsenic, with gas sweeping, preferably an oxidizing gas such as for example air, preferably for 0.1 to 48 hours, at a temperature of 200 to 800 ° C; this step is preferably followed by resulfurization (steps (c) and (d)).

The following examples illustrate the invention without limiting its scope.

EXAMPLE 1

(comparative)

One impregnates 1 kg of autoclaved alumina beads of 170 m² xg⁻¹ of specific surface and pore volume 1.2 cm³ xg⁻¹ with 1.2 l of an aqueous solution containing 370 g of copper nitrate trihydrate Cu ( NO₃) ₂, 3H₂O.

The alumina beads thus impregnated are dried and calcined for 7 hours at 400 ° C. under a stream of air at a VVH of 5000 h⁻¹. We obtain so-called basic beads for the rest of the experiment. The beads thus obtained are in another step not in accordance with the invention, impregnated with a bezel, using 1 l containing 0.52 l of water and 0.48 l of an aqueous solution at 20% by weight of sulphide. ammonium. The excess sulfur is removed by drying in an oven at 200 ° C for 10 hours under a stream of nitrogen (VVH 5000 h⁻¹).

The mass A obtained contains copper sulphide in an amount of 15% relative to the weight of the mass. X-ray diffraction analysis indicates that all of the copper is in the form of copper sulfide. Chemical analysis shows that the Cu / S atomic ratio is 1.0.

EXAMPLE 2

Exactly as in the first example, 1 kg of autoclaved alumina beads 170 m² xg⁻¹ of specific surface and pore volume 1.2 cm³ xg⁻¹ are impregnated with 1.2 l of an aqueous solution containing 370 g copper nitrate trihydrate. The alumina beads thus impregnated are dried and calcined for 7 hours at 400 ° C. under a stream of air at a VVH of 5000 h⁻¹.

Then we operate in accordance with the invention: the beads thus obtained (and said to be basic) are preheated to 70 ° C. and then in another step (corresponding to step (c)) impregnated with the beverage pan with an organic sulfur mixture comprising 90 g of micronized sulfur, the particles of which have an average diameter of 2 microns, partially dissolved in 1.1 liters of toluene at 70 ° C, the impregnation being carried out all at once, hot on the support preheated to 70 ° C.

The product is then dried at 120 ° C to remove most of the solvent (which is condensed and then recycled), then at 200 ° C (heat treatment in step (d) of the invention) for 10 hours under a stream of nitrogen. We observe that it emerges from SO₂.

Mass B obtained contains 15% copper sulphide, like mass A. X-ray diffraction analysis shows that all the copper is combined in the form of copper sulphide CuS. Chemical analysis shows that the Cu / S atomic ratio is 1.0.

Example 3

The preparation of the mercury capture mass is exactly as in the second example, replacing the aqueous solution containing 370 g of copper nitrate trihydrate with 365.3 g of copper nitrate trihydrate and 3.36 g of silver nitrate.

The mass C obtained contains 15% copper sulfide plus silver sulfide like the masses A and B previously described. X-ray diffraction analysis shows that all of the copper and all of the silver in mass C is in the form of a sulfide.

EXAMPLE 4

The mercury and / or arsenic A, B and C capture masses obtained in the previous examples are tested under the following conditions. The apparatus consists of a tubular metal reactor whose inactivity for the fixation of mercury has been controlled. 30 ml of the capture mass to be tested are introduced into this reactor and a stream of natural gas containing mercury is passed at a temperature of 50 ° C., under a pressure of 40 bars (4.0 MPa) to a VVH of 15,000 h⁻¹ (TPN, temperature and normal pressure) or a flow rate of 450 lxh⁻¹.

The centesimal volume composition of the natural gas to be purified is 84% ​​CH₄, 0.6% hydrocarbons having 5 and more carbon atoms in their molecule, the rest being made up of a mixture of N₂, CO₂, C₂H₄, C₃H₈ and C₄H₁₀. The mercury content in the gas entering the reactor is 4500 µ g / Nm³ (TPN).

The quantity of mercury remaining in the gases after purification is evaluated by a method using the principle of the variation of resistivity of a gold film amalgamated by mercury.

The efficiency of the capture masses is defined by the relationship.<maths id="math0006" num=""><math display="block"><mrow><mtext>E%</mtext><mfrac><mrow><mtext>(mercury content at inlet) - (mercury content at outlet) x100</mtext></mrow><mrow><mtext>(mercury content at entry)</mtext></mrow></mfrac></mrow></math><img file="EP0484234A2_D0006.tif" /></maths>

The so-called "initial" efficiency is determined after 10 hours of operation under the conditions described above.

Measurements are then carried out after 500, 1000 and 1500 hours of operation under the operating conditions described above.

The results are given in Table I below, they show that the masses obtained by the process of the present invention have a very good efficiency and that, moreover, their resistance over time is greater than that of the comparison mass A.

EXAMPLE 5

The starting product for the tests below is the so-called basic beads prepared in Examples 1, 2 and 3.

All the tests were carried out using these beads.

It will be recalled that the process developed according to the invention comprises several variants, the basic diagram being as follows: Mixing of the support loaded with copper oxide (that is to say so-called basic beads) with elemental sulfur in powder or granules. Heat treatment of this mixture between 140 ° C and 150 ° C in an inert atmosphere, for example steam or nitrogen. Possible additional treatment by impregnating the product thus obtained with dilute formic acid. Optionally final heat treatment (between 140 and 150 ° C) in an inert nitrogen or water vapor atmosphere.

Note

:

<ul id="ul0002" list-style="none"><li>a) When the last two steps are carried out before the first two steps, the same results are obtained.</li><li>b) Similar results are also obtained by carrying out certain steps simultaneously and in particular by carrying out the following diagram:<img file="EP0484234A2_D0007.tif" /><ul id="ul0003" list-style="none"><li>. Mixing of the support loaded with copper oxide (that is to say so-called basic beads) with elemental sulfur and simultaneous impregnation with dilute formic acid.<ul id="ul0004" list-style="none"><li>. Heat treatment of the mixture obtained at 140-150 ° C under inert gas, especially nitrogen.</li></ul></li></ul></li><li>c) We also obtain results of the same order of magnitude in the following process:<ul id="ul0005" list-style="none"><li>. Treatment of the support loaded with copper oxide by a reducing agent.</li><li>. Mixing of the support obtained loaded in copper with elemental sulfur.</li><li>. Heat treatment under inert gas, especially nitrogen, between 200 and 220 ° C.</li></ul></li></ul>

Heat treatment at a temperature above 200 ° C eliminates the loss on ignition at 200 ° C and transforms all the copper into copper sulfide.

Two industrial tests were also carried out:

The support loaded with copper oxide (so-called basic beads) is carefully mixed with elementary sulfur with a particle size between 0.5 and 1 mm from the Société des Soufres Industriels.

The mixture thus obtained is treated with a rotary steamer for 2 hours under a nitrogen atmosphere (Indust. N2 test) and a second test was carried out under water vapor (Indust. H2O test), under the above operating conditions.

Table II below summarizes all the results.<tables id="tabl0001" num="0001"><img file="EP0484234A2_D0008.tif" /></tables>

EXAMPLE 6

X-ray diffraction analyzes show that the copper oxide is not completely transformed into copper sulfide during heat treatment at 140-150 ° C. Only half of the oxide has been processed.

A. To complete this transformation, the following test was carried out:<ul id="ul0006" list-style="none"><li>1) The catalyst obtained after mixing with sulfur and heat treatment under nitrogen (or water vapor) was impregnated with a mixture containing 15% formic acid. The entire pore volume, about 60 cc per 100 g of catalyst, was impregnated.</li><li>2) The catalyst thus impregnat ed was treated at 140-150 ° C under nitrogen (or water vapor).</li></ul>

The results by X-ray diffraction analysis are conclusive: all of the copper oxide has been transformed into copper sulfide.

B. This treatment has been applied on an industrial scale with the following conditions:

The catalyst is impregnated to 20% of its pore volume with a 20% solution of formic acid, ie 120 l of formic acid diluted per ton of catalyst.

The catalyst was then treated under nitrogen (or steam) at 140-150 ° C in an oven of the Louisville type.

The results are identical to the laboratory tests.

EXAMPLE 7

The following tests were then carried out (in the laboratory):<ul id="ul0007" list-style="dash"><li>impregnation of the support loaded with copper oxide (so-called basic beads) with a dilute formic acid solution. The amount of formic acid used is the stoichiometric amount.</li><li>treatment at 140-150 ° C under nitrogen or water vapor.</li><li>mixing of the product obtained containing metallic copper with elemental sulfur.</li><li>heat treatment at 140-150 ° C under nitrogen or water vapor.</li></ul>

The results are identical to the previous tests, that is to say that the starting copper oxide is completely transformed into copper sulfide.

Example 8

As described in Example 4, the apparatus consists of a tubular metal reactor whose inactivity for the fixation of arsenic has been controlled. 100 ml of the capture mass to be tested are introduced into this reactor and a stream of natural gas containing arsenic is passed through at a temperature of 60 ° C., under a pressure of 35 bars (3.5 MPa).

Two capture masses were tested: the mass dried under nitrogen at a temperature between 140-150 ° C was tested at a VVH of 1015 h⁻¹ and the mass of industrial manufacture dried under nitrogen at a temperature between 140-150 ° C was tested at a VVH from 3045 h⁻¹.

In both cases, the collection mass bed was separated into five 12 g zones. The zone known as "zone 1" is the first to contact the load containing the arsenic.

The centesimal volume composition of the natural gas to be purified is 84% ​​CH₄, 0.6% hydrocarbons having 5 and more carbon atoms in their molecule, the rest being made up of a mixture of N₂, CO₂, C₂H₄, C₃H₈ and C₄H₁₀. The amount of arsenic in the gas entering the reactor is 1.607 x 107g per hour in both cases.

The quantity of arsenic remaining in the gases after purification is evaluated by difference between the quantity of arsenic in the charge (known) and the quantity of total arsenic detected in the capture mass after test by measurement of fluorescence-X.

The efficiency of the capture masses is defined by the relationship.<maths id="math0007" num=""><math display="block"><mrow><mtext>E% = 100- </mtext><mfrac><mrow><mtext>(weight As at entry) - weight As in mass) x 100</mtext></mrow><mrow><mtext>(weight As at entry)</mtext></mrow></mfrac></mrow></math><img file="EP0484234A2_D0009.tif" /></maths>

The results are given in the table below, they show that the use of the masses obtained by the process according to the invention have very good efficiency.<tables id="tabl0002" num="0002"><img file="EP0484234A2_D0010.tif" /></tables>

The process for preparing the mass for capturing mercury and / or arsenic for the subsequent use of this mass in a process for removing mercury and / or arsenic allows a solid mass to be obtained having better resistance over time, as well as the following main advantages:<ul id="ul0008" list-style="dash"><li>Possibility of incorporating the sulfurizing agent at a relatively low temperature, usually below 100 ° C.</li><li>Possibility of transforming the precursor of the capture mass of mercury and / or arsenic resulting from the incorporation of elemental sulfur, into an active capture mass, at a relatively low temperature usually below 250 ° C.</li><li>Use of a non-toxic sulfurizing agent with no bad smell.</li></ul>