MXPA99006555A - An improved procedure for the preparation of a sox reducer additive and its resultant product - Google Patents

Abstract

El procedimiento de síntesis del aditivo reductor de SOx, objeto de la presente invención tiene como originalidad la obtención de un aditivo de mayor capacidad de reducción del SOx, reflejado en un incremento substancial en la velocidad de adsorción y reducción, comparado con los materiales que actualmente se ofrecen comercialmente. En la preparación del aditivo en mención, se emplea arcilla como soporte y dispersante de la fase activa, en substitución parcial o total de la alúmina, lo que hace que disminuya su costo.

Description

IMPROVED PROCEDURE FOR THE PREPARATION OF A SOx REDUCING ADDITIVE AND RESULTING PRODUCT DESCRIPTION TECHNICAL FIELD OF THE INVENTION The present invention relates to an improved process for obtaining an SOx emission reducing additive in the catalytic disintegration units, FCC. This additive consists of a magnesium aluminate with spinel structure containing different concentrations of kaolin clay, which is obtained after mixing aqueous solutions of magnesium oxide compounds, with organic acids, especially acetic acids, clay in suspension and oxides. of cerium and vanadium. The mixture of magnesium oxide, alumina sol and kaolin, which previously peptized giving it an average particle size between 1-50μm, at a pH of the sun between 2.5-9.5. The sol obtained is homogenized by continuous agitation, between 5000-10000 rpm, during 0.5-10.0 h, obtaining a sol between 15-35% solid, which is spray dried forming particles of mesh between 100-300 μm, appropriate for the fluidized bed. The process of the present invention is characterized by the preparation of a magnesium oxyacetate in the form of sol, which is obtained after mixing the magnesium oxide compounds with formic or acetic acids dissolved in water. To this mixture is added an alumina sol, at room temperature with stirring; said sol is homogenized at an average particle size between 1-50 μm. To this gel is added kaolin in suspension, a solution of rare earths especially cerium nitrate and a solution of malate or vanadium oxalate, obtained by the interaction of maleic or oxalic acid with vanadium pentoxide. The obtained sun is spray-dried and calcined between 600-1000 ° C in air flow between 2.0-8.0 l / h, during 2-20 h.

The material obtained is used as an additive and / or catalyst for the removal or reduction of SOx emissions in the FCC catalytic disintegration units, contributing in this way to abate the contamination by sulfur compounds produced in these units.

BACKGROUND OF THE INVENTION The environmental impact produced by sulfur oxides emissions (SOx = SO2 + SO3) has received great attention in recent years. The Environmental Protection Agencies of both E. U and Europe, have imposed a limit for the SOx emissions of catalytic cracking units fluid type (FCCU), of 300 ppm, equivalent to 9.8 Kg of SOx / 1000 Kg of burnt coke . It is clear that the control of SOx emissions is of great importance for any refinery.

The amount of SOx emitted by the regenerator of an FCC unit is a function of the amount of sulfur in the load, the yield to coke and the conversion. From 45 to 55% of the sulfur in the load is converted to H2S in the FCC reactor, 35 to 45% remains in the liquid products, and 5 to 10% is deposited on the catalyst in the coke. This sulfur in the coke is the one oxidized to SOx in the regenerator of the FCC unit, generally a mixture of approximately 90% SO2 and 10% SO3.

The mechanism of SOx reduction occurs with any metal oxide or metal oxide types that can react with SOx to form the corresponding sulfate. In the regenerator, the sulfur carrier coke burns giving S02, CO, CO2 and water. A part of the SO2, in the presence of excess oxygen, burns even more to form SO3. SO3 can exist in the flue gas or react with the catalyst or with a metal oxide to form the metal sulfate.

The reaction to metal sulphate can be considered as the "capture reaction" of the SOx. When moving to the reactor, the metal sulfate will react with the hydrogen to form either metal sulfide and water or metal oxide, H2S and water. In the stripping, metal sulfide reacts with water vapor to form oxide of metal and H2S. Finally, the sulfur leaves the system in the form of H2S in the stream of product instead of SOx in the flue gas.

The oxides of sulfur SO2 and SO3, are toxic gases that by action of light Ultraviolet and atmospheric humidity can be transformed into sulfuric acid and generate the so-called acid rain, according to the following chemical reactions: SO2 + / 2O2 - so, so3 + y2H2o - H, SO__ For this reason it is necessary to implement technologies aimed at reducing or eliminating this type of emissions. In the case of the FCC catalytic disintegration units. The developed additive is a sulfur transfer agent that captures the SOx produced in the regenerator and releases H2S in the reactor and exhausting. SO3 is adsorbed on the metal oxide dispersed in the spinel.

The transformation of SO2 to SO3 is catalyzed by vanadium pentoxide (V2O5) and promoted by rare earth oxide and especially CeO2 cerium dioxide which acts as an oxygen accumulator and supplier.

SO2 + _o2 - > SO, CeO, The sulfur adsorbed on the metal oxide is released as H2S in the reactor and the exhausting, which regenerates the active species of the additive. The general mechanism of SOx reduction with the additive developed is as follows: Oxidation of SO2 (Regenerator) SO3 SO2 + MeO capture > • MeS04 Reaction of the metal sulphate (Reactor) MeSO4 + 4H, - MeO + H2S + 3H2O MeSO4 + 4H, - MeS + 4H2O Oxidation of metal sulphide (Exhaust) MeS + H2O - »MeO + H2S Both the absolute sulfur level of the charge and the types of sulfur compounds in it will affect SOx emissions. As the percentage (by weight) of sulfur in the cargo, the potential SOx emissions will also increase. Another important parameter of the load that affects SOx capture is the type of sulfur present in the load. The sulfur associated with the paraffins tends to disintegrate to form H2S thus leaving the system with the products of the reactor. However, the sulfur associated with the aromatic chains tends to be deposited as coke. Coke combustion increases SOx emissions. Therefore, to determine the effect of the higher sulfur content in the charge, it is necessary to know the types of sulfur compounds present.

It has been argued that the key properties of an additive, necessary to reduce SOx emissions are high metal oxide content accompanied by a large surface area of the support, to allow access to the metal oxide sites and the presence of a metal oxide promoter. the oxidation. A matrix rich in large surface metal oxides improves the SOx capture reaction. The net result of these characteristics of the additive is a high level of reduction of sulfur emissions.

The SOx removal mechanism is well known and has been reported by a good number of authors in documents such as: Kinet. Katal. 28 (1), 236 (1987), ACS, Division of fuel chemistry, Preprints V 39 No. 1, 238 (1994).

In the removal of SOx from the emissions of the catalytic cracking process, magnesium spinels with cerium and vanadium are currently used, as mentioned in: Appl. Catal. B: Environmental 1, 169 (1992), I & EC Res. 30, 1444 (1991).

The activity and mechanism of SOx removal of these materials are relatively well characterized, however, their efficiency depends on the composition and method of preparation. US Patent 5,108,979 (1992) covers a process for obtaining a SOx reducing additive in FCC using magnesium spinels as active components. The methodology of preparation of the Mexican patent No. 962302 (1996) leads to obtain an additive with components of spinel magnesium, magnesium oxide, cerium and vanadium, very efficient in the reduction of SOx in the FCC units.

The synthesis process of the SOx reducing additive, object of the present invention has as originality the obtaining of an additive with a greater SOx reduction capacity, reflected in a substantial increase in the speed of adsorption and reduction, compared with the materials that currently they are offered commercially. In the preparation of the aforementioned additive, clay is used as a support and dispersant of the active phase, in partial or total substitution of the alumina, which reduces its cost.

Considering the quality of the product obtained, the raw material used and the simplification of the operations involved, the preparation process, object of the present invention, represents a significant and original advance over other procedures and provides a wide variety of applications.

DETAILED DESCRIPTION OF THE INVENTION The detailed procedure of the present invention for the preparation and determination of the capacity of uptake of sulfur oxides in the materials object of the present invention was carried out according to the following steps: 1. Preparation The improved process object of the present invention for obtaining a low cost SOx and NOx emission reducing additive in FCC catalytic disintegration units is carried out in accordance with the following steps, which is not limiting the scope of the invention. this patent. In a first step, an aqueous magnesium source mixture is prepared, selecting the magnesium oxide and an organic acid, especially acetic acid, which is stirred vigorously at a temperature comprised between 30 and 100 ° C; on the other hand, a second aqueous suspension acidified also with organic acid is prepared, slowly adding alumina to said suspension, forming a gel, which peptizes into particles comprised between 1 -50 μm. This gel is mixed with the suspension of magnesium oxyacetate and clay, leaving a suspension at a pH between 2.5-9.5, to which is added rare earth salts, especially Ce (NO3) 3 »6H2O and vanadium pentoxide (V2O5) , introducing it to the mixture as a solution of vanadium oxalate at temperatures between 20-100 ° C. This suspension is homogenizes under agitation between 5000-10000 r.p.m., during 0.5-10.0 h., at a pH between 2.5-9.5 obtaining a sol between 20-40% solid. Later the sun resulting, obtained in the previous steps is spray dried at a high speed of injection of the dosing pump that varies between 10-50 cc / min, to a inlet temperature in the sprinkler between 200-350 ° C and outlet temperature between 75-115 ° C, obtaining solids in the form of microspheres, which are sieved in metal meshes of No. 100-325, obtaining a size of suitable particle to be used in a fluidized bed unit (UFCC).

This additive is calcined between 600-1000 ° C in air flow between 1.0- 10 l / h for 0.5-10 h.

The raw materials used in the preparation of the materials in question, are from industrial use, however the foregoing is not limiting, it being possible to resort to the use of other materials of natural origin or pure substances, especially when They want to obtain solids free of metal cations. The materials obtained by the The process of the present invention can be applied to gas streams containing SO2, from a few ppm, to very high concentrations (above 2% weight).

The product obtained by the mentioned process results in a material of reduced cost and easy obtaining with properties that make it attractive for industrial application, especially as a reducing additive for sulfur and nitrogen oxides in fluid catalytic cracking processes. 2. characterization of the materials The materials were characterized by X-ray diffraction after calcination determining its crystallographic phase. In the same way, the textural properties were determined by nitrogen adsorption at 77 K, using the BET equation. 3. Evaluation of SOx adsorption capacity. The adsorption of SO2 in the materials was measured in a gravimetric thermal analyzer, equipped with a manual set of valves to have a process of oxidation-reduction, adsorption and cleaning of the system. The test was performed with the following procedure: 1) 20 to 30 mg of catalyst was placed in a platinum basket on the TGA scale. 2) a process of cleaning and stabilization of the sample is carried out, heating at 20 ° C / min. up to 650 ° C in air atmosphere which flows at 20 cc / min. 3) after stabilizing the temperature at 650 ° C and purging the system with N2, the SO2 adsorption of a mixture of 1.5% SO2 gases is initiated in air, a mixture that is introduced at 20 cc / min. 4) Weight gain occurs until a maximum adsorption is reached, which can take, depending on the sample, between 60 and 90 min. It is then assumed that the weight gained is due to the SO3 adsorbed by the metals to form the respective metal sulphate, in this way the percentage of sulfur trapped by the catalyst can be calculated. 5) after the adsorption cycle of SO2 comes the reduction of the resulting sulphate, once the system has been cleaned with N2 the temperature is lowered to 550 ° C and the sample is reduced with a flow of H2 at 20 cc / min. until it completely evacuates (above 95%) the adsorbed SOx, this process lasts approximately 60 min. If the reduction is not complete at this temperature, the sample is heated to 650 ° C in the same H2 atmosphere, at this temperature the sample is completely reduced. 6) After the reduction, N2 flows for 10 min. at this same temperature (650 ° C) to eliminate the excess H2 in the line. The catalyst is reactivated in the presence of air for 30 min. A second SOx adsorption cycle can be carried out under the same conditions, as well as the reduction, thus forming a sequence of adsorption cycles. In this way, the stability of the catalyst is determined by repeating the adsorption-reduction-oxidation cycles.

After it is mixed between 1.0-10% weight with the FCC catalyst and deactivated with water vapor between 10 and 100% at a temperature between 600-1000 ° C for 1.0-10 h., Once deactivated they are tested their activity at pilot plant in the removal of SOx in the load containing about 2% sulfur, as well as in tests performed by gravimetric thermal analysis (TGA). n The use of this additive formulated with a magnesium aluminate, MgO and clay promoted with vanadium pentoxide and rare earth oxides, used alone or in a mixture of 0.5-5.0% by weight with the FCC catalyst, allows to control the emission of polluting gases that contain sulfur in both FCC units and in fixed sources of industrial processes, and in this way comply with environmental protection standards.

EXAMPLES Some practical examples related to the described procedure are described below, without thereby limiting the scope of the present invention.

EXAMPLE 1 The catalysts were prepared from a mixture of gels formed by the reaction of acetic acid with aluminum and magnesium oxides for the formation of spin it A suspension of kaolin from 50 to 60% solid was added at the same time, enough to obtain 0.0 to 64% clay in the catalyst. Solutions of Ce nitrate and vanadium oxalate were added to the mixture, calculated to obtain concentrations of 7-14% CeO2 and 2-4% V2O5. This procedure of own preparation of additives of this nature, is based on the integration of the components followed by a homogenization adjusting the suspension between and 40% solid to facilitate spray drying.

All the catalysts were spray dried and then calcined between 600-900 ° C in air flow for 4 to 15 h. In this drying method, a NIRO Mobile MINOR atomizer, which allows to obtain materials in an interval of particle size between 60 and 120 μm, suitable for handling in evaluation and characterization. The proportion of the components used in the preparation of the prototypes is presented in Table 1.

Table 1. Proportion of components in the preparation of the catalysts MgAI2O4'MgO-CeO2-V2O5 / Clay Component% Commercial Clay 0 10 20 30 50 64 DX MgO 36.2 32.5 29.2 25.5 18.1 18.4 38.9 AI2O3 45.8 41.3 36.3 31.8 22.9 0.0 44.3 CeO2 14.0 12.6 11.3 9.9 7.0 14.0 13.8 V205 4.0 3.6 3.2 2.8 2.0 4.0 3.0 Clay 0.0 10.0 20.0 30.0 50.0 63.6 0.0 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 (% dry basis weight, MgAI2O4 / MgO = 1) EXAMPLE 2 The solid obtained in each of the preparations according to example 1, was analyzed after heat treatment by X-ray diffraction. All samples prepared according to this example, present a pattern of microcrystalline diffraction, identifying the phases of CeO2, MgAI2O4 and MgO, with greater amorphous portion in high clay contents.

EXAMPLE 3 The surface area measured in each sample obtained as described in example, and after the heat treatment, suffered a significant decrease when the catalyst has a higher proportion of clay (p.50%). Although the clay has a low pore volume (0.16 cm / Vg), the variation of this parameter in the samples with clay is around 25% staying above 0.3 cm3 / g, as can be seen in table 2 Table 2. Textural properties of the compounds of MgAI2O4 • MgO-CeO2-V2O5-Clay Clay in the sample, Surface area Pore volume% weight (2 / g) cnrVg 0 222 0.41 10 194 0.38 20 185 0.34 30 166 0.36 50 101 0.30 * 64 33 0.16 * Sample without alumina EXAMPLE 4 The SOx adsorption capacity in the materials was carried out by thermogravimetry with a mixture of SO2 (1%) / air at 650 ° C. 20 mg was taken approximately with a particle size between 60 and 150 microns, the The procedure was carried out according to what was described above, obtaining a graph like the one shown in figure 1.

The total adsorption to full saturation of the material was obtained as well as the SOx adsorption per gram of MgO. The adsorption speed was estimated based on the weight increase monitored in the first 30 minutes of the test, results that can be seen in table 3.

Table 3. Total adsorption (% weight) and SOx adsorption per gram of MgO. SOx adsorption rate depending on the content of clay Commercial Prototype Time (min.) I II III IV V VI DX 1, 2 2.1 2.2 1, 8 1, 0 1, 1 1.6 4.5 6.0 6.4 5.9 4.9 5.1 4.5 7.9 10.0 10.6 10.0 8.9 9.4 7.4 1 1, 3 13.8 14.8 14,0 12.9 13.5 10.2 14.7 17.6 18.9 18.0 16.6 17.5 13.2 18.1 21, 4 22.9 21, 8 20.2 21, 2 16.1 Total adsorption 68.0 50.3 46.5 44.2 33.0 36.6 63.4 Speed Ads. 0.60 0.71 0.76 0.73 0.67 0.71 0.54 Ads / g MgO 0.50 0.66 0.78 0.85 1.1 1 1.15 0.42 The addition of clay to the additive decreased SOx adsorption in an equivalent ratio. It should be noted that all the solids had a total SOx uptake capacity greater than 90% (% weight) in relation to their total Mg concentration. For comparative purposes, a commercial additive (key DX) was studied.

Although the total uptake of SOx is related to the total Mg concentration, the difference between the solids is manifested in the rate of uptake. In this same table the percentage of adsorption of SOx per gram of MgO is presented, presenting a greater uptake in low MgO contents. In general, samples prepared with clay presented a higher adsorption rate, with a maximum observed at concentrations of 20-30%. The uptake speed of the commercial additive, DX, was significantly lower.

The results of total SOx adsorption showed that all Mg is available; The difference lies in the speed at which the process takes place. Obtaining higher speeds in materials that contain clay.

If it is considered that all Mg adsorbs SOx, using clay as support, this allows a better dispersion of the active components including CeO2 and V2O5, thus facilitating the formation of microcrystalline particles on the surface of the catalyst, accelerating the redox process, which It gives in the oxidation of SO2 to SO3 and later the reduction of the metal sulphate to H2S and metal oxide. The trends of the regeneration rate are also consistent with a scheme of better dispersion of the active components.

Although samples prepared with clay presented consistently lower surface area relative to spinel without clay, their rate of SOx adsorption was always higher, even when the sample does not contain alumina and consequently there is no formation of the spinel (MgAI2O4).

EXAMPLE 5 After saturation, the samples were subjected to purging with nitrogen and a treatment in 100% hydrogen current at 550 ° C until complete reduction. The additives experienced a weight loss recovering their original weight in a 95% The materials with clay and the additive MgAI2O4 * MgO-CeO2-V2O5 (without clay) reduced at comparable speeds, relatively higher for material with 30% clay. The supported MgO (64% clay) and the commercial additive were reduced to lower speeds, as shown in table 4. The speed of reduction and the percentage of reduction, was calculated based on the change in weight determined in the first 30 minutes.

Table 4. Reduction rate and% reduction of total SOx adsorbed on the catalyst, depending on the clay content.

Commercial Prototipc Time > (min.) I II III IV V VI DX 0.5 3.6 2.4 3.7 3.6 2.2 1.6 7.0 8.4 7.6 9.2 7.5 9.5 4.3 1 1, 5 13.4 12.9 15.2 12.5 15.6 6.6 16.9 18.1 17.8 20.7 16.4 19.1 9.0 23.1 22.5 22.8 26.3 20.8 21, 6 12.0 29.0 27.5 28.4 31, 7 25.2 23.5 16.2 Speed reduction 0.97 0.92 0.95 1.06 0.84 0.80 0.54 % Reduction 42.6 54.7 61.0 71.7 76.4 64.2 25.5 Adsorption and desorption rates are considered as parameters of great importance, related to the performance of this type of additives, considering the conditions and residence times in the FCC unit, especially in the stage of reaction.

EXAMPLE 6 To determine the stability of the materials, adsorption reduction cycles were performed in identical conditions of examples 4 and 5. In this test the sample containing 30% clay was used. The speed of adsorption and reduction was calculated in the first thirty minutes of each cycle, obtaining a behavior like the one shown in figure 2.

Claims (3)

NOVELTY OF THE INVENTION Having described the invention, it is considered as novelty and therefore Claims as property what is contained in the following clauses:

1. An improved process for the preparation of a SOx reducing additive, characterized in that it comprises reacting in an aqueous medium, a source of magnesium such as magnesium oxide, with an organic acid such as acetic acid or formic acid, at temperatures comprised between 30 and 100 ° C; preparing a second aqueous suspension acidified with an organic acid such as acetic acid or formic acid to which alumina is added, whereby a gel is formed, which is peptized into particles comprised between 1 and 50 μm; mix the gel thus formed, with a suspension of oxyacetate of magnesium and clay, at a pH of 2.5-9.5 add rare earth salts, such as Ce (N03) 3-6H2O and V2O5; homogenize the mixture to obtain a solid sun, dry the solid sun and calcining it.

2. An improved process according to clause 1, characterized in that the V2O5 is introduced into the reaction mixture, in the form of a solution, at temperatures of 20 to 100 ° C.

3. An improved process according to clause 2, characterized in that the resulting suspension containing Ce (NO3) 3.-6H2O and V2O5 is homogenized with stirring at 5000-10000 rpm, for 0.5 to 10.0 hrs., Thereby obtaining a sun with a solids content of 20-40%. An improved procedure in accordance with clauses 1 to 3, characterized in that the calcination is carried out at temperatures of 600-1000 ° C, in air flow at 1.0-10 / rirs., For 0.5 to 10 hrs.