WO2015074127A1

WO2015074127A1 - Hydrogen production method and catalyst

Info

Publication number: WO2015074127A1
Application number: PCT/BR2013/000504
Authority: WO
Inventors: Roberto Carlos PONTES BITTENCOURT; Luiz Eduardo MAGALHÃES CORREA DA SILVA; Maira ANDRADE RODRIGUES; Cecilia PEREIRA RODRIGUES; Carlos Otavio BRITO; Fernanda DE CARVALHO MUNIZ BOMBARDELLI
Original assignee: Petróleo Brasileiro S.A.-Petrobras
Priority date: 2013-11-22
Filing date: 2013-11-22
Publication date: 2015-05-28
Also published as: AR098331A1; BR112014017691A2; BR112014017691B1

Abstract

The present application discloses a method for producing hydrogen by catalytic decomposition of ammonia from acid water units. In a first step, the ammonia stream is purified in contact with various catalytic beds, removing chlorides and sulfur, and more specifically, ammonia is partially transformed into hydrogen in the bed formed by a catalyst based on alkalis and alkaline earths, supported on zinc oxide, alumina, silica-alumina and mixtures thereof, with nickel oxide as the active phase. In the second step, the purified ammonia stream is fed to the steam reforming reactor to generate hydrogen which is then purified. The application also relates to the catalyst used in the method.

Description

Hydrogen production process and catalyst

FIELD OF INVENTION

The present invention finds its field of application among the processes for the production of hydrogen by catalytic decomposition of ammonia solutions. More specifically, the catalytic production of hydrogen from ammoniacal gaseous streams generated in the acid water unit resulting from hydrocarbon hydrotreating processes.

BACKGROUND OF THE INVENTION

Petroleum is composed of a complex mixture of hydrocarbons, associated with varying contents of organic compounds containing nitrogen, sulfur and oxygen and smaller amounts of metals such as vanadium, nickel, sodium, calcium and copper.

Oil processing generates numerous derivatives, including gasoline, diesel and aviation kerosene.

Compounds such as sulfur, nitrogen, oxygen, halogens and metals are classified as undesirable in derivatives because along the consumption chain they generate atmospheric pollutants and alter the integrity of equipment and the derivative itself.

To ensure quality and compliance with current legislation, it is usual to refer these derivatives to a treatment called "hydrotreating", whose characteristic is to alter or remove the impurities present in these derivatives by the use of hydrogenation reactions.

For hydrocarbons having sulfur and nitrogen contaminants, hydrogenation reactions generate hydrogen sulfide (H ₂ S) and ammonia (NH ₃ ). These reactions occur in fixed bed filled reactors that use catalysts manufactured mostly from nickel (or cobalt) and molybdenum sulfides, supported mainly by alumina.

During the hydrotreating process the injection of water, which occurs prior to the separation between the excess hydrogen used at the stoichiometry of the hydrogenation reactions and the process products. The goal of water injection is to retain hydrogen sulfide and ammonia in aqueous solution. This avoids the deposition of salts such as ammonium sulfide (NH ₄ SH) which could clog lines and equipment after deposition if present in the hydrocarbon stream. The aqueous solution thus obtained constitutes an effluent called "acid water".

In addition to hydrotreating, various processes in the refining industry also generate acidic water. Examples are distillation, catalytic cracking, hydrocracking, thermal cracking and delayed coking.

The acid water stream contains contaminants that make it impossible to release it directly into the environment or reuse it in refining processes. For this to occur, it is usual for this effluent to be treated in a specific unit called the "acid water unit" for the removal of hydrogen sulfide and ammonia. Multiple configurations of acid water units are found in the specialized technical literature. The acid water stream is rectified, and gaseous streams containing ammonia and hydrogen sulfide are generated.

One method routinely employed for the final treatment of these ammoniacal gas streams generated in the acid water unit is incineration.

In the petroleum industry, the Claus process is the standard method for eliminating sulfur from gaseous effluents. It comprises a first thermal (or combustion) step and a second catalytic (or catalytic bed) step.

Sulfur compounds present in the ammonia stream are incinerated in the burners of a Claus process unit to recover sulfur. The thermal step reactions of the Claus process are: H ₂ S + y ₂ o ₂ → so ₂ + H ₂ O

2NH ₃ + 3/20 ₂ → N ₂ + H ₂ 0

In the catalytic step, sulfur oxide (SO ₂ ) reacts with the remaining hydrogen sulfide, represented by the following reaction:

2H ₂ S + S0 ₂ → S + 2H ₂ 0

The sulfur thus recovered is sold in liquid or solid state.

Injection of the ammoniacal gas stream recovered from the acid water unit into a Claus unit may be a convenient method of disposing of this effluent. However, it does produce some obstacles, such as the difficulty in controlling the ratio of sulfur dioxide and hydrogen sulfide concentrations in the combustion section, particularly when the ammonia stream contains hydrocarbons. This ratio is a critical factor for the correct operation of the unit. Additionally, carbon dioxide (C0 ₂₎ formed in combustion of hydrocarbons or previously existing in the ammonia stream, lead to loss of sulfur recovery efficiency. Ammonia that is not incinerated has the potential to form exit deposits in equipment such as ammonium sulfides, compromising the efficiency or campaign time of the unit. At the same time, partial incineration can generate a high emission of environmentally harmful nitrogen oxides (NO _x ) subject to restrictions under environmental legislation.

An additional difficulty faced with the use of ammonia currents in Claus units in the prior art is limited to a maximum ammonia addition value relative to the total processed charge of about 30% to 35% on wet basis.

Some oils occurring in Brazil are characterized by high levels of nitrogenous compounds, for example, the one exploited in the Campos Basin. As a consequence, the acid water unit produces a lift gas with ammonia content lift.

One technical solution to circumvent this situation is combined incineration: using the Claus unit to the limit established by the technique, and directing excess ammonia to a dedicated incinerator.

Although known from the state of the art, incineration of the ammonia stream from the acid water unit, either in a Claus type unit or in a dedicated incinerator, does not generate products that can be traded.

Different processes for the recovery of ammonia present in acidic water streams are found in the specialized technical literature. Ammonia can be recovered directly in anhydrous form or in aqueous solution, or indirectly in the form of sodium hydrosulfide, ammonium thiosulfate, ammonium sulfate and ammonium phosphate.

Of particular importance to the oil industry is the recovery of ammonia through its transformation into hydrogen, as this is a large-scale input used in hydrotreating processes. Currently, for the production of hydrogen, natural gas and naphtha are preferably used, which are high-cost but multi-purpose raw materials. The first, used in the energy matrix, the second, raw material in the petrochemical plants.

The most widely used process for producing large scale hydrogen in the refining industry is steam reforming. Hydrocarbons react with water vapor at high temperatures and pressures. Nickel-based catalysts are used in refractory supports of alpha-alumina, magnesium aluminates and calcium aluminates.

In large capacity units, the hydrocarbons used in addition to natural gas and naphtha are refinery gases, propane and butanes. Taking methane as an example, the main reactions are represented by the equations below, which together have a balance highly endothermic.

CH ₄ + H ₂ O → CO + 3H ₂ (endothermic, 206.4 kJ / mol).

CO + H ₂ 0 → CO ₂ + H ₂ (exothermic, - 41.2kJ / mol).

The steam reforming process is usually conducted by introducing a previously purified charge into a variable number of fixed bed reactors. Such reactors are constructed of metal tubes, typically 7 cm to 15 cm in diameter and 10 m to 13 m high, located inside a heating furnace that supplies the heat needed for the reactions. The reactor and furnace assembly is called the primary reformer. The typical inlet temperature of the gases to be processed in the primary reformer reactors is in the range of 400 ° C to 550 ° C, and the outlet temperature in the range of 750 ° C to 950 ° C at typical pressures in the range. from 10 kgf / cm ² to 35 kgf / cm ² .

The ammonia decomposition reaction, thermodynamically favored by the use of high temperatures, is represented by the equation:

NH ₃ → 1.5H ₂ + 0.5N ₂

According to the technical literature, under reaction temperatures above 527 ° C and a pressure of 1.9 bar, the thermodynamic equilibrium predicts a conversion greater than 99.5%.

Decomposition of ammonia into hydrogen and nitrogen can be performed on a variety of catalysts, such as those based on platinum (Pt), rhodium (Rh), palladium (Pd), iridium (Ir) and nickel (Ni). It is known and used in industrial practice that decomposition of ammonia can be performed by nickel-based catalysts under the conditions of the primary reformer. Such decomposition can be used for the initial reduction of catalysts supplied as nickel oxide, according to the equations below:

NH ₃ → 1.5H ₂ + 0.5N ₂

H ₂ + NiO / holder → Ni / holder + H ₂ 0 Technical literature and industry practice also teach that nickel-based catalysts used in the primary reformer are highly susceptible to poisoning deactivation. Most common contaminants are sulfur, arsenic, phosphorus, lead and halogens. These should be reduced to levels below 0.1 ppm, preferably below 0.01 ppm to achieve adequate catalytic activity and therefore a campaign time of at least 3 years.

The aqueous stream that is treated in the acid water unit contains hydrogen sulfide and ammonia in contents ranging from 300 ppm to 20,000 ppm, with ammonia to hydrogen sulfide ratios in the range 1 to 2.0. This stream may further contain other contaminants such as hydrocarbons, chlorides, sulfates, formates, cyanides, cations such as sodium, potassium and calcium, mineral or organic acids and dissolved gases such as carbon dioxide and oxygen in varying concentrations.

The gaseous stream that is generated in the acid water unit, in addition to contamination by sulfur compounds such as hydrogen sulfide and mercaptans, also has other contaminants, sometimes below analytical detection limits, but sufficient to cause deactivation of sulfur catalysts. primary reform. Potential contaminants are inorganic and organic chlorine compounds. Chlorides can significantly reduce the activity of steam reforming catalysts.

US 2007/0178034 discloses a process for removing organic and inorganic sulfur compounds from an ammonia stream. Sulfur is removed by a catalytic absorbent fixed bed composed of a catalyst with nickel mass ranging from 10% to 30%. The catalyst support is chosen from alumina, silica, titania, magnesium, zirconia or a mixture thereof. The promoter is chosen from the oxides of the chemical elements cerium, praseodymium, neodymium, promethium, samarium or a mixture thereof. Methanation catalysts are indicated as preferred. The ammoniacal current after The sulfur removal is mixed with a hydrocarbon stream and is employed for hydrogen generation in a steam reforming process. The purification method presented herein is specific for the removal of sulfur compounds. An ammoniacal current generated in an "acid water" unit contains a plurality of other contaminants.

EP 0096970 discloses a process for removing organic sulfur compounds such as hydrogen sulfide, mercaptans, sulfides and disulfides present in ammonia streams generated in the processing of hydrocarbons, oil shale and coal. Sulfur is removed in a zinc oxide bed at a reaction temperature in the range of 260 ° C to 454 ° C. However, no mention is made of the purification of other contaminants or of their use for hydrogen production.

US 7,258,848 discloses a process for treating gases containing ammonia and hydrogen sulfide. Ammonia is removed by washing the gases with a strong acid, for example concentrated sulfuric acid, to convert the ammonia to a salt. The aqueous solution or crystallized ammonia salt may be employed as fertilizer.

Thus, the purification processes of ammonia currents generated in acid water units are specific for the removal of sulfur compounds. The prior art lacks a process that removes other contaminants, such as halogen compounds, metals and hydrocarbons, and results in an ammoniacal current which, employed in a catalytic reforming process for hydrogen production, leads to a reduced rate. of catalyst deactivation.

SUMMARY OF THE INVENTION

The object of the present invention is a process for the production of hydrogen by catalytic decomposition of ammonia solutions. from acid water units. Such a process involves the purification of an ammonia stream and the use of this purified stream as a charge in a steam reforming process. The purification step removes impurities such as sulfur, halogens, metals and olefin hydrocarbons. The purified stream is fed to a reforming furnace, which is part of the steam reforming process, for the conversion of ammonia to hydrogen.

Additionally, a catalyst is synthesized, whose characteristics make it possible to use it to purify the ammonia current with a low deactivation rate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for producing hydrogen by catalytic decomposition of ammonia solutions from acidic water units. The objective is achieved by a process carried out in two main steps, namely: a first ammonia current purification step comprising a pretreatment of the ammonia current in a plurality of catalyst beds, and a second step, which consists in the submission of the treated current to the steam reform.

Additionally, to perform the process, a catalyst is synthesized, the characteristics of which enable its use in the purification step of the ammoniacal current.

Generally speaking, the invention is a continuous process for the production of hydrogen, carried out in two steps:

The first step comprises the following steps:

- remove metals and chlorides in the gaseous ammonia stream from acidic water units in a first bed consisting of materials chosen from alumina, silica-alumina, silica, titanium, magnesium, zirconium and mixtures thereof, maintained at a reaction temperature in 300 ° C range 650 ° C under pressure in the range 1 kgf / cm ² to 40 kgf / cm ² to obtain a first stream of effluent;

- transform organic chloride and sulfur compounds, contaminants of the first effluent stream, into hydrochloric acid and hydrogen sulfide, and additionally hydrogenate olefinic compounds into a second bed consisting of hydrotreating catalysts chosen from cobalt-molybdenum and nickel. supported on alumina and alternatively supported on zinc oxides at a reaction temperature in the range 300 ° C to 650 ° C under pressure in the range 1 kgf / cm ² to 40 kgf / cm ² to obtain a second effluent stream;

removing hydrogen sulfide and inorganic chlorine compounds such as hydrochloric acid, ammonium chloride and additionally partially transforming ammonia into hydrogen and nitrogen into a third bed consisting of catalysts promoted by materials selected from alkali metals and alkaline earth based on materials chosen from zinc oxide, alumina, silica alumina and mixtures thereof and having nickel oxide as the active phase at a reaction temperature in the range 300 ° C to 650 ° C under pressure in the range 1 kgf / cm ² to 40 kgf / cm ² to obtain a third stream of effluent;

- removing inorganic and organic sulfur and chlorine compounds from the third effluent stream in a fourth bed consisting of catalysts selected from those containing zinc and copper oxides at a reaction temperature in the range 300 ° C to 650 ° C, under pressure in the range of 1 kgf / cm ² to 40 kgf / cm ² to obtain a purified ammonia current;

The second step comprises the following steps:

- feed the purified ammonia current into a reactor for 4

Producing hydrogen by the steam reforming process to obtain a hydrogen rich gas stream;

purifying the hydrogen rich gas stream to obtain the final hydrogen product.

The present invention can be applied to existing hydrogen production units by the steam reforming process by simply adapting the pretreatment section of the existing unit to the plurality of beds.

In addition to the ammonia stream, a hydrocarbon stream can also be fed in the first process step. The hydrocarbon stream corresponds to the charge that is normally employed in industrial hydrogen production units by the steam reforming process. The ammoniacal current corresponds to a fraction of the hydrocarbon charge and is in the range of 1% to 10% by volume. Hydrocarbons may be chosen from natural gas, liquefied petroleum gas, naphtha and a mixture thereof in any proportion.

In the purification process, hydrogen is preferably added to the filler to prevent coke formation in the second catalytic bed.

In the third bed, the inclusion of nickel oxide in the catalyst formulation enables the partial transformation of ammonia to hydrogen and nitrogen. The catalyst is synthesized containing nickel oxide as the active phase, supported by materials chosen from zinc oxide, alumina and a mixture thereof, and promoted by materials chosen from alkaline and alkaline earth metals.

The catalyst is obtained by dry impregnation technique from the impregnation of a support selected from alumina and zinc oxide with a metal hydroxide solution to obtain a material of type K / alumina or K / ZnO. . The material is dry and calcined. The calcined material is then impregnated with nickel nitrate solution, dried and calcined again, giving rise to the catalyst whose characteristics allow its use for the purification of the ammonia current with a low deactivation rate. Catalyst synthesis will be presented in detail below.

The fourth bed is composed of materials that can be chosen from zinc and copper oxides in contents above 50% by mass. For example, commercial low temperature shift (LTS) catalysts known in the art by the term "low temperature shift" used in steam reforming hydrogen production processes may be used.

The beds used in the first stage are mounted inside reactors. Each reactor contains a single bed type, totaling four beds and four different reactors. Alternatively, the plurality of beds may be contained in a single reactor. The arrangement of beds in a single or several reactors is determined by the volumetric capacity of the unit and the relative costs of the equipment. The volume of each bed should be selected according to the content of contaminants present in the ammonia stream, as well as the campaign time projected for an industrial unit.

The use of the first and second beds in an industrial configuration of the present invention is determined by the type of contaminants present. Thus, in a metal free load, the use of the first bed is not necessary. In a load free of organic sulfur, the use of the second bed is not necessary. The use of the fourth bed for the final removal of inorganic and organic compounds containing sulfur and chlorides is determined by the contaminant content allowed in the product, as well as the objective campaign time of the reformer of an industrial unit.

In the second stage of the process, steam reforming, purified ammonia current is routed to a pre-reformer, and, alternatively, to a primary reformer, commonly employed in the steam reform process. In these devices, the residual ammonia from the third bed is converted into hydrogen and nitrogen. The stream obtained after the conversion reaction shall be treated to remove impurities mixed with hydrogen.

The treatment methods employed are known from the state of the art. The reduction of carbon monoxide (CO) content occurs by the displacement reaction. The removal of carbon monoxide, carbon dioxide, methane and nitrogen occurs by the use of a pressure variation adsorption system (PSA).

The catalyst developed according to the present invention is employed in the third bed being capable of decomposing ammonia and simultaneously removing chloride (Cl) and sulfur (S) from the ammonia stream. The catalyst can be chosen from an alumina supported catalyst, promoted by an alkaline or alkaline earth metal, preferably potassium, and with an active phase of nickel oxide (NiO / K / alumina) and a zinc oxide supported catalyst by an alkaline or alkaline earth metal, preferably potassium, and with an active nickel oxide phase (NiO / K / ZnO). In addition to alumina and zinc oxide, silica alumina or mixtures thereof may be used as a support.

The alkali metal content employed in the catalyst is in the range 1% to 7% by weight, preferably 2% to 4% by weight. The nickel oxide content employed in the catalyst is in the range of 5% to 40% by weight, preferably between 10% to 20% by weight. Catalysts with specific area in the range of 15 m ² / g to 30 m ² / g are obtained.

For catalyst synthesis procedures known in the art are employed and described in detail in the examples illustrating the present invention.

EXAMPLE 1: Synthesis of NiO / K / alumina catalyst.

In this example the alumina-supported catalyst was synthesized, promoted by potassium and active phase of nickel oxide (NiO / K / alumina).

The catalyst was prepared with two hundred grams of Pural SB alumina hydroxide (Condea Chemie), impregnated with an aqueous solution of 11.5 grams of potassium hydroxide (KOH) by the dry impregnation technique (pore volume technique). The material thus obtained was dried at temperatures in the range of 100 ° C to 120 ° C for a period of time in the range of 8 hours to 12 hours and calcined at temperature around 600 ° C for a period of time around 4 ° C. hours After this time, the calcination temperature was raised to around 1,200 ° C for a time of about 1 hour to obtain a K / alumina type material.

One hundred and thirty-three grams of K / alumina material was impregnated with an aqueous solution containing 27.2 grams of nickel nitrate hexahydrate [Ni (N03) 2.6H20] by dry impregnation technique (pore volume technique). followed by drying at a temperature in the range of 100 ° C to 120 ° C for a period of time in the range of 8 hours to 12 hours and calcined at a temperature of around 450 ° C for a period of about 4 hours to obtain a NiO / K / alumina catalyst. The catalyst thus obtained had a concentration of 3% by weight of potassium (K), 15% by weight of nickel oxide (NiO) and a specific area of 27,7 m ² / g determined by the nitrogen adsorption technique.

The catalyst is employed for ammonia conversion and removal of chloride and sulfur.

EXAMPLE 2: Synthesis of NiO / K / ZnO Catalyst.

In this example the potassium-promoted zinc oxide support catalyst and nickel oxide active phase (NiO / K / ZnO) were synthesized.

The catalyst was prepared with one hundred and fifty grams of a commercial zinc oxide impregnated with an aqueous solution of 3.01 grams of potassium hydroxide (KOH) by pore volume technique. The material thus obtained was dried at a temperature of about 110 ° C and calcined at a temperature of about 450 ° C for a period of about 4 hours to obtain a K / ZnO type material.

Ninety grams of the K / ZnO material was impregnated with an aqueous solution containing 19.5 grams of nickel nitrate hexahydrate [Ni (NO3) 2.6H20] by pore volume technique, followed by drying at temperatures in the range of 100 ° C. ° C to 120 ° C for a period of time in the range of 8 hours to 12 hours and calcined at a temperature of around 450 ° C for a period of about 4 hours to obtain a NiO / K / ZnO material . The catalyst thus obtained had a concentration of 2% by weight of potassium (K) and 15% by weight of nickel oxide (NiO) and a specific area of 17,2 m ² / g determined by the nitrogen adsorption technique.

EXAMPLE 3: Catalyst Performance - Chloride Retention.

In this example the chloride retention capacity of the catalysts of the invention prepared according to Examples 1 and 2 was compared to commercial catalysts used in prior art processes. A first selected catalyst is a commercial nickel-based catalyst. A second catalyst selected for the low temperature shift (LTS) step in the steam reforming hydrogen production process is a commercial CuO / ZnO / AI ₂₀ type catalyst.

The experiments were performed in a laboratory scale process unit, containing a catalyst fixed bed reactor and employing the following experimental conditions:

- atmospheric pressure;

- temperature of 350 ° C;

- Catalyst mass equal to 2,0 g; particle size less than 0.105 mm or 150 mesh.

The catalysts were initially pretreated under hydrogen flow at a temperature of 400 ° C for a period of 60 minutes and then cooled to a temperature of 350 ° C.

The experiment consists of passing a flow of 40 mL / min. of hydrogen in a saturator containing concentrated hydrochloric acid PA kept at a temperature of 10 ° C and feed it to the reactor.

The catalysts are compared over time to observe the appearance of chloride in the reactor effluent. An average hydrogen chloride solution concentration of 34% was assumed (corresponding to a vapor pressure of hydrogen chloride on the solution of 26.4 mmHg according to the tabulated values in the literature). The time for chloride "leakage" to occur was used to estimate chloride retention capacity (kg Cl / kg material).

The reactor effluent was followed by mass spectrometry, monitoring the fragment with a mass / charge ratio of 36.

Results are presented in Table 1 below.

According to Table 1, the material synthesized in Example 1 has a 75% higher chloride retention capacity than the commercial methanation catalyst (base case). The catalyst synthesized in Example 2 has an 875% higher chloride retention capacity relative to the commercial methanation catalyst.

EXAMPLE 4: Catalyst Performance - Sulfur Retention.

In this example the sulfur holding capacity of the catalysts of the invention prepared according to Examples 1 and 2 was compared to prior art catalysts. The selected commercial catalysts were the same as those employed in Example 3.

The experiments were performed in a laboratory scale process unit, employing the following experimental conditions:

- atmospheric pressure;

- temperature of 350 ° C;

- catalyst mass of 3,0 g; particle size less than 0.105 mm.

Sulfur was fed to the reactor by passing an 8 ml flow per minute of a gas mixture containing 15% hydrogen sulfide in hydrogen. The presence of hydrogen sulfide was detected in the reactor effluent by the use of ampoules for the detection of hydrogen sulfide, known as the Drager ampoule. The catalysts are compared over time to observe the appearance of sulfur in the reactor effluent and this value used to estimate sulfur retention capacity (kg S / kg material). Results are presented in Table 2 below.

TABLE 2

Example 1 Example 2 Catalyst Catalyst

CATALYST

NiO / K / alumina NiO / K / ZnO LTS methanation

Escape Time

25 149 54 164 Sulfur (minutes)

Capacity of

Retention (kg S / kg 0.037 0.219 0.079 0.241 material)

According to Table 2, the material synthesized in Example 2 has 177% higher sulfur retention capacity than the commercial methanation catalyst.

The commercial catalyst LTS according to the process of the present invention can be used to make up the plurality of acid water stream purification beds as it has 200% superior chloride retention capacity and superior sulfur retention capacity. 205% over the methanation catalyst.

These examples illustrate the increased chloride and sulfur retention capacity of the catalysts prepared according to the present invention as compared to prior art catalysts. EXAMPLE 5: Catalyst Performance - Ammonia Decomposition.

In this example the ammonia decomposition activity of catalysts of the invention prepared according to Examples 1 and 2 was compared to prior art catalysts. The selected commercial catalysts were the same as those employed in the previous examples.

- atmospheric pressure;

- temperature in the range from 450 ° C to 550 ° C;

- catalyst mass equal to 0,5 g; particle size less than 0.105 mm.

The catalysts were initially pretreated under hydrogen flow at 450 ° C for a time period of 60 minutes. Ammonia was fed to the reactor by passing flow rates in the range of 10 mL / min. at 40 mL / min. of hydrogen in a saturator containing concentrated ammonium hydroxide PA at a concentration in the range of 28 to 30% ammonia maintained at a temperature of 10 ° C. The reactor effluent was monitored by mass spectrometry, monitoring the fragments with the mass / charge ratio of 17 and 28 for ammonia and nitrogen, respectively.

The catalysts are compared for ammonia conversion activity (%) by varying the hourly space gas velocity (GHSV) parameter and the reaction temperature, as shown in Table 3 below.

The results from Table 3 show that the catalyst synthesized in the

Example 1 shows greater decomposition activity of ammonia in hydrogen and nitrogen than observed in the methanation catalyst. Both catalysts exhibit significant ammonia decomposition activity only at temperatures above 450 ° C.

According to the present invention, it is not necessary for the decomposition reaction of ammonia to occur simultaneously with the treatment of the stream to remove contaminants such as sulfur and chloride, as such reaction will occur downstream of the purification step in primary reform stage of the hydrogen production process by steam reforming. In certain situations, however, such as limited volume of the primary reforming catalyst or high flow rate of ammonia in admixture with the hydrocarbon stream, it is desirable that part of the transformation of ammonia to hydrogen occurs simultaneously with the removal of contaminants such as chlorides and sulfur. Therefore, it is possible to reconcile a high contaminant holding capacity with a high partial conversion of ammonia by employing bed mixtures of materials synthesized according to Examples 1 and 2 and LTS catalyst.

The results confirm the great potential of the application of the process for hydrogen production by catalytic decomposition of ammonia solutions, as well as the potential for ammonia current purification by the synthesized catalyst.

The examples demonstrate that chloride retention can be increased by up to 875% and sulfur retention by up to 177% by using the catalysts synthesized in the present invention over commercial methanation catalysts. The commercial catalyst LTS which according to the present invention can be used to make up the plurality of acid water stream purification beds has 200% higher chloride holding capacity and 205% higher sulfur holding capacity. regarding commercial methanation catalysts.

Therefore, the advantages of the present invention in relation to the state of the art, as follows:

- provides a relatively low cost method for the purification of ammonia currents from acidic water units;

- provides the purification of ammonia currents with high concentration of contaminants;

- makes it possible to produce hydrogen from streams with a high concentration of ammonia and other contaminants using a catalytic steam reforming process; and - can be applied to already installed large-scale hydrogen production units by the steam reforming process without the need for additional capital costs.

Although the present invention has been described in its preferred embodiment, the main concept underlying the invention remains preserved as to its innovative character, where those of ordinary skill in the art may envision and practice appropriate variations, modifications, alterations, adaptations and equivalents. and compatible with the working environment in question, without, however, departing from the scope of the spirit and scope of the present invention, which are represented by the following claims.

Claims

1. Hydrogen production process, characterized by comprising the catalytic decomposition of ammonia solutions from acidic water units, carried out in two stages, being a first stage of purification of the ammonia stream promoted in a plurality of catalytic beds, and a second stage. steam reforming of the purified ammonia stream, according to which:

The first step of purifying the ammoniacal current comprises the following steps:

- remove metals and chlorides from the ammonia stream in a first bed, consisting of materials chosen from alumina, silica alumina, silica, titanium, magnesium, zirconium and mixtures thereof, maintained at a reaction temperature in the range 300 ° C to 650 ° C, under pressure in the range 1 kgf / cm ² to 40 kgf / cm ² , to obtain a first stream of effluent;

- remove hydrogen sulfide and inorganic chlorine compounds such as hydrochloric acid, ammonium chloride, contaminants from the second effluent stream and additionally partially transform the ammonia into hydrogen and nitrogen into a third bed, consisting of catalysts promoted by materials selected from alkaline and alkaline earth metals, supported on materials chosen from zinc oxides, alumina, silica-alumina and mixtures thereof, and having nickel oxide as the active phase at a reaction temperature in the range from 300 ° C to 650 ° C under pressure in the range 1 kgf / cm ² to 40 kgf / cm ² to obtain a third stream of effluent;

The second step comprises the following steps:

feeding the purified ammonia stream into a reactor for the production of hydrogen by the steam reforming process to obtain a hydrogen rich gas stream;

purifying the hydrogen rich gas stream to obtain the final hydrogen product.

Hydrogen production process according to claim 1, characterized in that the ammonia solution stream corresponds to between 1% and 10% by volume of the hydrocarbon feedstock fed to the process.

Hydrogen production process according to claim 1, characterized in that the arrangement of the beds is determined by the volumetric capacity of the unit and the volume of each bed is selected as a function of the contaminant content present in the ammonia stream.

4- CATALYST FOR HYDROGEN PRODUCTION by catalytic decomposition of ammonia solutions from acid waters characterized by catalysts promoted by materials chosen from alkaline and alkaline earth metals, supported on materials chosen from zinc oxides, alumina, silica-alumina and mixtures thereof, and having nickel oxide as the active phase, such catalyst being employed in at least one catalytic bed of a hydrogen production process according to claim 1.

Hydrogen production catalyst according to Claim 4, characterized in that it is synthesized by dry impregnation of a support selected from alumina, zinc oxide or mixtures thereof with a solution of at least one hydroxide. alkali metal or earth alkaline, having incorporated nickel oxide as the active phase.

Hydrogen production catalyst according to claims 4 and 5, characterized in that the catalyst particles obtained have a specific area in the range 15jn ² / g and 30 m ² / g.

Hydrogen production catalyst according to claims 4 and 5, characterized in that the alkali metal content employed in the catalyst is in the range of 1% to 7% by weight and the nickel oxide content employed in the catalyst is in the range. 5% and 40% by mass.

8. Hydrogen production catalyst according to claim 6, characterized in that the alkali metal content is between 2% and 4% by mass.

Hydrogen production catalyst according to claim 6, characterized in that the nickel oxide content is between 10% and 20% by mass.

Hydrogen production catalyst according to claim 4, characterized in that it is synthesized by dry impregnation of a support selected from alumina, oxide of zinc, or mixtures thereof, with a solution of at least one alkali metal hydroxide or earth alkali having nickel oxide as the active phase.

Catalyst for the production of hydrogen according to claim 4, characterized in that the catalyst synthesis comprises the following steps:

- impregnating alumina hydroxide with an aqueous potassium hydroxide solution, and drying the material at temperatures ranging from 100 ° C to 120 ° C for a period of time ranging from 8 hours to 12 hours;

- calcining the material at a temperature of around 600 ° C for a period of time of about 4 hours;

- raise the calcination temperature to around 1,200 ° C for a period of time around 1 hour to obtain a K / alumina material;

- impregnating the K / alumina material with an aqueous solution of nickel nitrate hexahydrate, and drying the material at temperatures in the range 100 ° C to 120 ° C for a period of time ranging from 8 hours to 12 hours;

- calcining the impregnated material at a temperature of around 450 ° C for a period of time of about 4 hours; and

- raise the calcination temperature to around 1,200 ° C for a period of time around 1 hour to obtain a NiO / K / alumina catalyst.

- impregnate the zinc oxide with an aqueous potassium hydroxide solution, and dry the material at a temperature around 110 ° C; calcining the material at a temperature of about 450 ° C for a period of time of about 4 hours to obtain a K / ZnO material;

- impregnating the K / ZnO material with an aqueous nickel nitrate hexahydrate solution, and drying the material at temperatures in the range 100 ° C to 120 ° C for a period of time ranging from 8 hours to 12 hours;

calcining the impregnated material at a temperature of about 450 ° C for a period of about 4 hours to obtain a NiO / K / ZnO catalyst.