ES2315179B1 - AN ABSORBENT COMPOSITION CONTAINING ALPHA - SEPIOLITE, ENSTATITA OSUS BLENDS, METHOD OF OBTAINING AND USE. - Google Patents

Abstract

An absorbent composition containing α-sepiolite,
enstatita or its mixtures, method of obtaining and use.

The present invention relates to a composition of an absorbent material characterized in that comprises sepiolite, enstatite or mixtures thereof with carbonates, hydroxides or oxides of alkaline or alkaline earth elements and their mixtures These materials may be shaped as granules; pills spheres; mass cylinders; hollow cylinders type smooth or striated macaroni, straight, curved, regular cut or irregular in any shape and size; or plates; also refers to its use in the purification of gases generated by systems of combustion as an absorbent material for gases and acid vapors in fixed and mobile beds.

Description

An absorbent composition that contains α-sepiolite, enstatite or mixtures thereof, method of obtaining and use.

Technical sector

The invention relates to new materials absorbents and their use in the elimination of acid gases.

State of the art

During the last decades, the environment it has been seriously damaged by the phenomenon called acid rain; atmospheric deposition of acidic compounds has caused the eutrophication of lakes, acidification of surface waters and the impoverishment of agricultural land by leaching from nutrients. Also, acid rain produces a negative effect about the health of humans, animals and plants and even It deteriorates buildings and monuments in urban areas.

Sulphurous anhydride and oxides of nitrogen, which are the compounds, along with ammonia, that more they contribute to the formation of acid rain, they are generated mainly in units that incinerate fossil fuels or Their derivatives.

The elimination of these undesirable compounds present in the flue gases has been the subject of numerous studies and technological developments in order to avoid their emission to the atmosphere.

As an example, recently it has been proposed the use of aqueous solutions of hydrogen peroxide for removal of traces of sulfur dioxide with acid formation sulfuric, KR 20050084454; the use of a Claus catalyst to the reduction of sulfurous anhydride with carbon monoxide, WO / 2004/067153, or a variation of the Claus process by reaction catalytic with sulfuric acid WO / 2004/105922. In the last years some proposals are intended to eliminate NO_ {2} and SO_ {2} simultaneously; thus, in KR 8.001.275 the use is described of ultrasound to form aerosols of both compounds that subsequently they are removed from the gas by precipitators electrostatic and in the US 6,936,231 a discharge is used electric to oxidize the NO to NO2 and subsequent washing of the gases with an ammoniacal solution.

Among the numerous records of new processes desulfurization include those that develop catalytic pathways to oxidize the SO2 to SO3. The most catalysts used in these systems are activated carbon JP 07.241.441, vanadium pentoxide supported on titania EP 622.106 or the eutectic formed by potassium thiosulfate and vanadium pentoxide supported on silica ES 9,601,955. These catalytic processes have proven very useful when gases are high temperatures, such as the conditioning of the gases of combustion in coal-fired power plants to improve efficiency of electrostatic precipitators.

Within the technologies developed for the sulphurous anhydride removal, suspension treatment aqueous carbonates, hydroxides and oxide of alkaline elements and alkaline earth or its mixtures is the process used in most of desulfurization facilities.

In these processes SO_ {2} is absorbed in the water and the acid formed must be neutralized to allow the SO_ {2} absorption continue. The speed at which this occurs neutralization determines how quickly SO2 is absorbed in the liquor.

When sodium compounds are used or magnesium the alkalinity of the liquid phase is high and, therefore, neutralization does not limit the absorption rate of SO2 from the gas phase; in this situation, the absorption kinetics of SO_ {2} is controlled by the effectiveness of the interaction between the gas and liquid phases (particle size, surface external drops, degree of turbulence, etc.) and can use the dry way that operates by particle atomization alkaline on the gases to be treated.

In its most widespread form this process Use calcium carbonate. The poor solubility of this compound limits the concentration of calcium cations in water and therefore the neutralization rate of the absorbed SO2; consequently this reaction turns out to be the controlling step of the global process In these wet processes, it is necessary employ high liquid / solid ratios, great times of contact and eventual addition of additives to maintain the pH of the system.

Despite its widespread implementation, this wet track technology presents major problems Technological The undesirable deposition of solids in the walls of deposits or pipes and frequent blockages of the nozzles and ducts; both phenomena undesirable are caused by the oxidation of calcium sulphite to Calcium sulfate (gypsum) due to the oxygen present in the gases to be treated Also, the construction materials of these units are exposed to the effects of corrosion phenomena, erosion and abrasion, especially in areas of contact with suspensions, muds or grouts used in the process.

Other added difficulties are management and treatment of surplus mud and water from the process, which they must comply with the regulations in force in each country for their discharge.

To avoid these difficulties have been proposed numerous procedures CA 1,107,037 describes a methodology that uses fly ash to limit deposition of solids on the surface of the absorber. In US 4,690,807, US 5,362,458 and US 6,221,325 replace the aqueous suspensions of solid compounds by an ammonium sulfate solution, where the sulphite and ammonium bisulfite formed are oxidized to sulfate and bisulfate ammonia which, by treatment with ammonia, is transformed into ammonium sulfate in two reactive stages. In US 4,035,470 it use copper or iron compounds to inhibit the oxidation of sulphite to sulfate.

Most of the registered proposals improve aspects of the process, although, in many cases, they increase the complexity of the system and the difficulty of its operation.

Description of the invention

The present invention relates to new absorbent materials and use in the elimination of gases acids

The present invention relates to a composition of absorbent / reactant material characterized in that comprises enstatite or α-sepiolite or mixtures of both silicates together with other components selected from: carbonates, hydroxides or oxides of alkaline elements or alkaline earth or its mixtures.

Said composition can be shaped as granules, tablets, spheres, mass cylinders, hollow cylinders, plates, or in parallel channel structures along the axis longitudinal in a number greater than 2 and less than 100 channels per square centimeter of cross section generally called monolith or honeycomb.

Said composition is preferably formed as hollow cylinders. These hollow cylinders can be of the type "macaroni" smooth, striated, straight, curved, regular cut or irregular, in any shape and size. Macaroni can have a length of about 0.5 cm to about 10 cm, and the wall thickness can be between about 0.04 cm and about 0.5 cm

According to a particular preferred embodiment the composition comprises α-sepiolite and algae limestone

According to a particular preferred embodiment the composition comprises enstatite obtained by heat treatment of the α-sepiolite and calcium oxide obtained by decomposition of the calcareous algae.

The new absorbents of the present invention they present textural properties that will allow the design and operation of absorption units in high dynamic regime Efficiency and low cost.

The present invention further relates to a method to prepare the composition defined above, characterized in that it comprises the following phases:

a) mix powders α-sepiolite and alkaline components up to obtain a homogeneous powder mixture,

b) knead the homogeneous powder mixture obtained with the addition of water to obtain a wet paste,

c) shape the wet paste in the desired way until you get the pieces,

d) air-formed parts dry and room temperature for at least 2 hours and between 80 and 270ºC at less for 2 hours,

e) heat treat the parts at temperatures between 400 ° C and 1000 ° C, preferably between 500 ° C and 900 ° C, for at least 2 hours.

       \ vskip1.000000 \ baselineskip
    

According to a preferred embodiment of the method, this It comprises the following phases:

a) mix powders α-sepiolite and limestone algae until obtaining a homogeneous powder mixture,

b) knead the homogeneous powder mixture obtained with the addition of water to obtain a wet paste,

c) shape the wet paste in the desired way until you get the pieces,

d) air-formed parts dry and room temperature for at least 2 hours and between 80 and 270ºC at less for 2 hours,

e) heat treat the parts at temperatures between 400 ° C and 1000 ° C, preferably between 500 ° C and 900 ° C, for at least 2 hours, preferably for at least 4 hours.

According to this embodiment, preferably, in phase a) they are mixed α-sepiolite and calcareous algae in a relationship weight between 1: 1 and 1: 5.

According to this embodiment, obtaining the absorbent materials are [cam carried out by forming of pastes prepared in aqueous medium with a mixture of powders α-sepiolite and limestone algae without the adding any other additive or component at any stage of its preparation. It is, therefore, two natural products, toxicity free Also, the pieces once saturated with Acid gases can be handled very easily as significantly increase its mechanical strength.

The present invention also relates to the use of a composition as defined above, as adsorbent material for purification of liquids, gases and vapors. Also, this material can be used as a neutralizing agent or remineralizing for water treatment, lowering its content in CO2 and supplying the carbonate and bicarbonate ions necessary.

The natural α-sepiolite used as raw material in this invention is α-sepiolite in compact form, and has been supplied by Tolsa, S.A. It is a magnesium silicate hydrated, whose structural formula is Si_12 Mg8 O30 (OH) 4 (OH2) 4 · 8H2 O.

Zeolitic channels open to the surface of the α-sepiolite create a network of pores of different sizes and dimensions and give it a surface specific greater than 200 m 2 g -1. The character hygroscopic of this material is due to its high number of silanoles and water molecules groups coordinated with the magnesium. Also, the facility is remarkable for this application exchanging magnesium cations with water protons. The disaggregated particles of this dry material have a size of 90% less than 0.3 microns; the texture has a total volume of pores of 0.35-0.40 cm 3 g -1 with a very significant development of mesoporosity (pores in diameter between 8 and 50 nm), with low microporosity values (pores of diameter between 0-2 nm) that are estimated at values of about 0.02 cm 3 g -1.

The calcareous algae used in this invention has been supplied by Algarea Minaraliçao Industria e Comercio Ltda. (Brazil) and corresponds predominantly to the species Lithothamnium SP . The average value of its weight composition is 90.9% calcium carbonate, 3% magnesium as Mg and 0.75% silica as SiO2. The rest corresponds to compounds of more than 20 elements present in small quantities. 90% of the disaggregated particles of this dry material have a size of less than 5 microns. The porous texture of this material has an average specific surface area of 6 m 2 g -1 with textural development centered on macroporosity (pores with a diameter of 50-10,000 nm) and absence of micropores. When the calcareous algae is treated at temperatures of 600 ° C or higher, CO2 is released with formation of the corresponding oxides of calcium and magnesium and the specific surface area of the material decreases to 2.6 m 2 g -1 }

Any invention may be used in this invention. limestone algae regardless of origin or procedure extraction with a disaggregated particle size, comprised between 2 and 100 microns preferably with 90% less than 5 microns

Heat treatments of the shaped material and dry at temperatures below 500ºC give rise to parts too sensitive to abrasion and crumbling physical structure by effect of water. When the formed and dry material is treated at temperatures between 500 ° C and 700 ° C a loss of water or hydroxyl groups of the α-sepiolite that dehydrates so irreversible, and part of the carbonates are transformed into oxides with release of CO2. At temperatures of 750ºC-800ºC all carbonates decompose and at temperatures between 830ºC and 900ºC, for a time not less than 2 hours, a new crystalline phase of silicate appears of magnesium called enstatite, ASTM 11-0273, whose empirical formula is Mg 2 Si 2 O 6 which surprisingly significantly increases the properties mechanics of the shaped material and makes it structurally very Stable to the action of water or water vapor.

The shaped and stabilized parts thermally present a high content of new pores of large diameter, mainly caused by the gaps or interparticular spaces that originate during kneading, forming and drying of these materials. That is, in these new absorbent compounds not only provide textural properties the two raw materials but also a macroporosity is formed of interparticular origin that increases the external surface area and therefore it promotes the phenomena of transport of matter in the interface (aspect of great importance in the absorption units in dynamic regime).

The formation of enstatite does not produce variations significant in the porous structure of the compound or its Absorption capacity. Thus, structured compounds in the form of hollow cylinders 15 mm long, 5 mm outside diameter and 3 mm inside diameter, prepared with α-sepiolite and calcareous algae in the ratio weight 1: 2, gave rise to absorbents that after being treated for 2 hours at temperatures of 800ºC and 850ºC had a rupture pressure of 0.6 kg and 1.1 kg per linear centimeter respectively. In both cases the ability to Absorption was 0.14 g of SO2 per gram of absorbent.

When instead of the calcareous algae are used other carbonates, oxides or alkaline absorbent hydroxides are they get significantly lower results. But nevertheless, when a part of the calcareous algae is replaced by coal activated, in certain cases there is a slight increase in absorption, possibly due to the catalytic effect of coal that enables oxidation of SO2 to SO3 in the presence of oxygen and water In these cases the weight ratio of α-sepiolite, alkaline components and carbon activated may vary between 1: 2: 0 and 1: 1: 1.

For the preparation of the materials object of this invention is mixed, dry and homogeneously, according to a preferred embodiment, powders α-sepiolite and calcareous algae; later, The mixture is kneaded with water in a high shear kneader. The elementary acicular particles of the α-sepiolite are normally found forming beams When these particles are properly kneaded in an aqueous medium (or in any other polar solvent) the space between the beams it widens, housing inside molecules of solvent mainly due to hydrogen bonds between surface silanole groups and solvent molecules. When limestone algae particles are also present during kneading, this mass of pseudoplastic character incorporates with great ease, producing the intimate mixture of both compounds The dough obtained after kneading is molded or Extruded to obtain the desired shapes and subsequently dried preferably at room temperature for at least 2 hours and at 80-270 ° C, for at least two hours; subsequently the material is heat treated between 400ºC-1000ºC, preferably between 500 and 900ºC for at least 2 hours in air or in an inert atmosphere in the case that part of the calcareous algae has been replaced in part by activated carbon.

When the wet mass obtained in the kneading preferably it is formed in hollow cylinder structures of suitable dimensions, materials with high are obtained operational benefits for the absorption of acid gases in dynamic regime This allows the treatment of large volumes of gases with minimal pressure losses through the use of mobile bed absorption units. These new units of absorption do not present problems of undesirable deposits or bindings, and are not significantly affected by corrosion, erosion and abrasion phenomena so frequent in conventional units.

Examples of embodiment of the invention

The present invention is further illustrated. through the following examples, which are not intended to be limiting its scope.

Example 1

Calcareous algae is used as raw material supplied by Algarea Minaraliçao Industria e Comercio Ltda. (Brazil) and α-sepiolite from Tolsa, S.A .; both materials in powder form.

After drying at 150 ° C for 24 hours, the α-sepiolite has a surface specific 217 m 2 g -1 with an outer surface of 121 m 2 g -1 and the calcareous algae has a specific surface of 5.9 m 2 g -1 and an external surface area of 5.6 m 2 g -1.

250 g of dry α-sepiolite with particle size 90% disaggregated <0.3 µm with 750 g of dry calcareous algae with 90% disaggregated particle size <5 \ mum. One time obtained a homogeneous mixture, this is taken to a dough mixer double sigma and kneading begins by slowly adding water deionized; the addition of water is completed, kneading is maintained During 4 hours. The mass thus obtained is formed by a extruder to obtain hollow cylinders 10 mm long, 4.5 mm outside diameter and 2.5 mm inside diameter. The pieces shaped, air dried and room temperature for 24 hours and then treated at 150 ° C for 3 hours in atmosphere of air and at 800 ° C for 2 hours in atmosphere of air.

The hollow cylinders thus obtained have a specific surface area of 9 m 2 g -1, with a surface external of 8 m 2 g -1, a volume of micropores negligible, a volume of mesopores of 0.03 cm 3 g -1 and a macropore volume of 0.52 cm 3 g -1. The properties obtained cylinder mechanics allow its use industrial and its structure proved to be perfectly stable against to water or water vapor.

       \ vskip1.000000 \ baselineskip
    

Example 2

The material prepared in the previous example is test to determine its absorption capacity in regime dynamic. The tests are carried out at temperatures of 20-24ºC and near atmospheric pressure. The air to be treated contains 4% molar of water and 650 ppm of SO2. Be operates at a spatial velocity of 2014 h <-1> and a velocity linear passage of gases through the bed of 0.8 Nm \ cdots -1. The absorption of SO2 that is measured up to 25 ppm output concentration turns out to be 0.21 g of SO2 per gram of absorbent.

After the tests the weight of the macaroni is increases by 40-50% and its resistance to Compression increases by 100%.

       \ vskip1.000000 \ baselineskip
    

Example 3

Following the procedure outlined in the Example 1 cylinders are prepared using the same materials premiums with the addition of activated carbon Fluesorb B obtained at from carbon by steam activation and supplied by Chemviron presenting a specific surface area of 1,093 m 2 g -1, a micropore volume of 0.42 cm 3 g -1, and a volume of mesoporos of 0.22 cm 3 g -1 and a size of 90% disaggregated particle <12.3 µm. To do this they mix 250 g of α-sepiolite, 500 g of calcareous algae and 250 g of activated carbon. Once a homogeneous mixture is obtained the procedure set forth in example 1 is followed.

The material obtained is tested in the conditions indicated in example 2, resulting in a capacity for absorption of 0.22 g of SO2 per gram of absorbent.

The size classification -micro, meso and macro- used in this document is the one adopted by the IUPAC "Manual of Symbols and Terminilogy of Physicochemical Quantities and Units "E. Butterworths. London (1972). The values of pore volumes and specific surface of materials are determined by mercury intrusion and by adsorption of nitrogen following the BET method.

Claims (13)

1. A composition of an absorbent material characterized in that it comprises α-sepiolite, or enstatite or mixtures thereof together with carbonates, hydroxides and oxides of alkaline and alkaline earth elements or mixtures thereof. 2. A composition of an absorbent material where carbonates, hydroxides and oxides of alkaline elements and alkaline earth or its mixtures may have mineral origin or organic. 3. A composition of an absorbent material according to claim 1, wherein said composition is formed as granules, pellets, spheres, cylinders mass, hollow cylinders or plates. 4. A composition of an absorbent material according to claim 3, characterized in that said hollow cylinders are selected from smooth cylinders of regular or irregular cut, fluted cylinders of regular or irregular cut, straight cylinders of regular or irregular cut and curved cylinders of regular cut or irregular 5. A composition of an absorbent material according to claim 1, characterized in that said composition is formed as a structure of parallel channels along the longitudinal axis in a number greater than 2 and less than 100 channels per square centimeter of cross section. 6. A composition according to claim 1 characterized in that it comprises α-sepiolite and calcareous algae or the derivatives obtained by treating these materials at temperatures above 600 ° C and below 900 ° C for at least 2 h in air. 7. A composition according to claim 6 where the α-sepiolite powder used in its preparation has a particle size of 90% less than 0.3 microns and limestone algae powder used in its preparation It has a particle size of 90% less than 5 microns. 8. A composition according to claim 1 which it can also comprise active carbon in proportions not greater than 33% by weight of the total. 9. A method for preparing a composition defined in claims 1 and 8 characterized in that it comprises the following phases: a) mix powders α-sepiolite of the alkaline components and possibly activated carbon until a mixture of powders is obtained homogeneous, b) knead the homogeneous powder mixture obtained with the addition of water to obtain a wet paste, c) shape the wet paste in the desired way until you get the pieces, d) air-formed parts dry and room temperature for at least 2 hours and between 80 and 270ºC at less for 2 hours, e) heat treat the parts at temperatures between 400 ° C and 1000 ° C, preferably between 500 ° C and 900 ° C, for at least 2 hours in air or in an inert atmosphere if It contains activated carbon. 10. A method according to claim 9, characterized in that in step a) α-sepiolite, alkaline components and activated carbon are mixed in a weight ratio that can vary between 1: 2: 0 and 1: 1: 1. 11. A method for preparing a composition defined in claims 1 and 6, characterized in that it comprises the following phases: a) mix powders α-sepiolite and limestone algae until obtaining a homogeneous powder mixture, b) knead the homogeneous powder mixture obtained with the addition of water to obtain a wet paste, c) shape the wet paste in the desired way until you get the pieces, d) air-formed parts dry and room temperature for at least 2 hours and between 80 and 270ºC at less for 2 hours, e) heat treat the parts at temperatures between 400 ° C and 1000 ° C, preferably between 500 ° C and 900 ° C, for at least 2 hours, preferably for at least 4 hours. 12. A method according to claim 10, characterized in that in step a) α-sepiolite and calcareous algae are mixed in a weight ratio between 1: 1 and 1: 5. 13. Use of a composition defined and characterized in the preceding claims as absorbent material for gases and acid vapors present in gases emitted by combustion units.