Granular moisture absorber based on natural layered aluminosilicates

Abstract

FIELD: moisture absorbers.SUBSTANCE: invention relates to granular dehydrators for moisture-comprising gases. A granulated moisture absorber based on natural layered aluminosilicates is proposed, including granulated bentonite with a montmorillonite content of at least 85% by weight, a granule size of 1.5–4 mm and a moisture content of 2–6%, and porous adsorbents – activated carbon and silica gel with the following ratio of components, % by weight: bentonite clay 40–99; activated carbon 0.5–60; silica gel 0.5–60.EFFECT: environmentally and hygienically safe granulated aluminosilicate moisture absorber used to reduce air humidity in industrial and domestic premises.1 cl, 5 ex

Description

[0001] Technical field

[0002] The invention relates to the development and use of granular dehydrators for moisture-containing gases, both natural (air) and hydrocarbon.

[0003] Prior Art

[0004] A method for preparing a highly effective alumina desiccant is disclosed in invention patent RU 2666448, published September 7, 2018. This method is characterized by producing an adsorbent with an optimal porous structure, acid-base surface properties, and chemical composition, including sodium, potassium, and barium, which are introduced during the peptization stage of pseudoboehmite-containing aluminum hydroxide. The technical result is the use of this alumina desiccant in dynamic water adsorption, which ensures increased stability of the adsorbent's sorption properties in multiple sorption / desorption cycles. The claimed desiccant has several disadvantages associated with the high cost of the preparation technology, relatively low sorption capacity for water vapor, and insufficient strength and polydispersity of the granules.

[0005] Natural desiccants based on aluminosilicate materials are more effective. For example, a known sorbent, disclosed in invention patent CN 113024270, published on June 25, 2021, contains plant fiber, attapulgite or bentonite, and calcium chloride. The preparation method involves mixing suspensions of attapulgite (or bentonite) and plant fibers in a specific proportion, adding a calcium chloride solution, followed by dispersion and rapid freezing, followed by lyophilization to produce a composite material that regulates humidity. The disadvantages of this technology include the high cost of producing the desiccant, as well as the limited shelf life of the material due to the use of plant fibers in the formulation.

[0006] A number of authors propose the use of hygroscopic inorganic salts deposited on a porous substrate. For example, patent RU 2174870, published October 20, 2001, discloses a mixture of lithium and calcium chlorides, both hygroscopic substances, applied to a porous base consisting of ground silica gel bound into strong, water-resistant granules by various mineral binders. The mixture is then impregnated with a solution containing 5-25% by weight of calcium and lithium chlorides. This method enables the production of a sorbent with a high dynamic capacity for water vapor. Silica gel is formed using an inorganic binder (silicic acid sol, aluminum hydroxide, bentonite clay, etc.), which is mixed with coarse-porous silica gel ground to a fraction of 5–50 microns to form a plastic paste, which is extruded into granules with subsequent drying of the resulting product.The claimed method is characterized by high energy consumption and ecological and hygienic limitations due to the use of strong electrolytes in the formulation, which are unacceptable in a number of contact drying technologies, when the desiccant comes into direct contact with humans or with natural components of the environment.

[0007] The use of porous substrates based on natural zeolite is presented in a desiccant sorbent disclosed in patent application US 2005 / 107,243, published May 19, 2005, which contains a hygroscopic salt and other traditional additives. The application also discloses a method for preparing said desiccant and variants of its use in thermally insulating window units, as well as as interlayers for thermally insulating window units. Sodium zeolite with a faujasite-type structure is preferred. The desiccant also contains clay, such as montmorillonite, kaolinite, bentonite, smectite, attapulgite, sepiolite, and any mixtures of these clays. The disadvantage of this invention is the need to use inorganic potassium salts as a filler for zeolite pores, which negatively affects the adsorption capacity of the clay component of the desiccant.

[0008] The closest in terms of the set of essential features to the claimed invention is a desiccant based on bentonite clay, described in the patent for invention RU 2744661, published on 12.03.2021, which includes natural sodium bentonite clay containing at least 80% montmorillonite with a dispersion of no more than 7.5 mm, as well as 5 - 15% by weight of powder and / or granules up to 2.5 mm in size of calcium chloride.

[0009] The desiccant presented in the closest analogue has the following disadvantages:

[0010] 1. Low rate of relative humidity reduction. This is because the prototype uses sorbents (bentonite and calcium chloride) with chemically similar mechanisms of aqueous phase sorption, which binds into hydrate shells of exchangeable cations of alkaline and alkaline earth elements. This method of moisture absorption has a variable rate and quickly slows down, reaching saturation.

[0011] 2. The use of calcium chloride in the desiccant reduces the environmental safety of the desiccant and significantly limits its use in domestic premises.

[0012] 3. Due to the presence of hygroscopic alkaline earth metal salts in the formulation, for the dehydration of which an elevated temperature is required, the desiccant has a very mediocre ability to regenerate, since the use of excessively high regeneration temperatures (above 120 о C) promotes overdrying of the bentonite component, which thereby loses its ability to adsorb the aqueous phase.

[0013] Disclosure of invention

[0014] The problem that the present invention is aimed at solving is the development of granular dehydrators for moisture-containing gases, both natural (air) and hydrocarbon.

[0015] The technical result achieved by implementing the present invention is an environmentally and hygienically safe granular aluminosilicate moisture absorber used to reduce air humidity in industrial and domestic premises.

[0016] The specified technical result is achieved due to the fact that the granular moisture absorber based on natural layered aluminosilicates includes bentonite clay and a porous adsorbent, wherein granulated bentonite with a montmorillonite content of at least 85% by weight, a granule size of 0.5–2 mm and a moisture content of 2–6% is used as the bentonite clay, and activated carbon and silica gel are used as the porous adsorbent in the following ratio of components, % by weight:

[0017] Bentonite clay: 40 – 99;

[0018] Activated carbon: 0.5 – 59.5;

[0019] Silica gel: 0.5 – 59.5.

[0020] Bentonite granules used in the desiccant are produced using bentonite raw materials containing at least 85% montmorillonite by weight, ensuring high moisture absorption and swelling properties of the bentonite particles. Water vapor absorption occurs through the hydration of the exchangeable interlayer alkaline and alkaline earth cations of the bentonite.

[0021] Activated carbon has a highly developed adsorption surface area from 500 to 2500 m 2 / g. This process involves physical adsorption of the aqueous phase, accompanied by condensation of water vapor in the fine capillaries of the adsorbent. This sorption mechanism ensures a rapid reduction in relative air humidity and a corresponding decrease in the dew point to the technologically optimal range below 20°C (under standard conditions).

[0022] Silica gel, being a polar adsorbent, has a developed specific surface area of ​​750 – 800 m 2 / g and holds water molecules by forming hydrogen bonds through the hydrogen atoms of the surface hydroxyl groups.

[0023] Thus, the claimed invention utilizes the synergistic effect of three water vapor adsorption mechanisms: hydration of alkaline and alkaline earth cations of the bentonite exchange complex, condensation of water vapor in the capillaries of activated carbon, and chemisorption of water molecules on the silica gel surface due to the formation of hydrogen bonds. The mutual enhancement of the adsorption activity of the adsorbent complex is due to the penetration of bentonite exchange cations into the pores of silica gel and the capillaries of activated carbon, increasing the adsorption capacity for water by 5-10 times, compared to individual adsorbents. This effect of mutual enhancement of adsorption properties is significantly reduced as the bentonite concentration in the sorbent complex decreases below 40%, since the diffusion of exchange cations into the pores and capillaries of activated carbon and silica gel is critically slowed.In addition, when the total concentration of porous sorbents (activated carbon and silica gel) decreases to less than 1%, the synergistic effect of increasing water vapor sorption also becomes less noticeable due to the lack of a sufficient number of adsorption-active micropores and capillaries in the complex.

[0024] The preparation of granular desiccant is carried out in several stages: crushing and fractionating lump bentonite clay, drying and re-fractionating the granules, mixing the bentonite granules with activated carbon and silica gel.

[0025] Example 1. Lump bentonite clay containing 85% montmorillonite is crushed and fractionated to obtain granules in the range of 0.5 - 2 mm. The granules are then dried in a drying oven at 120 °C to a residual moisture content of 2% by weight. After drying, the granules are re-fractionated in the range of 0.5 - 2 mm, fixing the median particle size close to 1.5 mm, and then mixed with activated carbon (particle size 0.5 - 3 mm) and silica gel (particle size 0.5 - 3 mm) in the following proportion: granulated bentonite - 99% + activated carbon - 0.5% + silica gel - 0.5%.

[0026] Example 2. Lump bentonite clay containing 90% montmorillonite is crushed and fractionated to obtain granules in the range of 0.5 - 2 mm. The granules are then dried in a drying oven at 120 ° C to a residual moisture content of 2% by weight. After drying, the granules are re-fractionated in the range of 0.5 - 2 mm, fixing the median particle size close to 1.5 mm, and then mixed with activated carbon (particle size 0.5 - 3 mm) and silica gel (particle size 0.5 - 3 mm) in the following proportion: granulated bentonite - 40% + activated carbon - 30% + silica gel - 30%. The composition must be provided in

[0027] Example 3. Lump bentonite clay containing 90% montmorillonite is crushed and fractionated to obtain granules in the range of 0.5 - 2 mm. The granules are then dried in a drying oven at 120 °C to a residual moisture content of 2% by weight. After drying, the granules are re-fractionated in the range of 0.5 - 2 mm, fixing the median particle size close to 1.5 mm, and then mixed with activated carbon (particle size 0.5 - 3 mm) and silica gel (particle size 0.5 - 3 mm) in the following proportion: granulated bentonite - 40% + activated carbon - 0.5% + silica gel - 59.5%.

[0028] Example 4. Lump bentonite clay containing 85% montmorillonite is crushed and fractionated to obtain granules in the range of 0.5 - 2 mm. The granules are then dried in a drying oven at 120 °C to a residual moisture content of 2% by weight. After drying, the granules are re-fractionated in the range of 0.5 - 2 mm, fixing the median particle size close to 1.5 mm, and then mixed with activated carbon (particle size 0.5 - 3 mm) and silica gel (particle size 0.5 - 3 mm) in the following proportion: granulated bentonite - 40% + activated carbon - 59.5% + silica gel - 0.5%.

[0029] Example 5. Lump bentonite clay containing 85% montmorillonite is crushed and fractionated to obtain granules in the range of 0.5 - 2 mm. The granules are then dried in a drying oven at 120 °C to a residual moisture content of 2% by weight. After drying, the granules are re-fractionated in the range of 0.5 - 2 mm, fixing the median particle size close to 1.5 mm, and then mixed with activated carbon (particle size 0.5 - 3 mm) and silica gel (particle size 0.5 - 3 mm) in the following proportion: granulated bentonite - 70% + activated carbon - 15% + silica gel - 15%:

[0030] The proposed granular desiccant based on layered aluminosilicates has the following advantages compared to its closest analogue:

[0031] 1. The use of porous sorbents in the new desiccant ensures a rapid reduction in relative air humidity through the combined action of chemisorption and condensation mechanisms of water vapor sorption. Thus, Composition 1, Composition 2, Composition 3, and Composition 4, under standard conditions, reduce relative air humidity from 85% to 75%, respectively, 1.5, 1.7, 1.8, and 1.5 times faster than the closest analogue, as documented in patent RU 2744661.

[0032] 2. This new desiccant, unlike its closest analogue, does not contain hygroscopic strong electrolytes (alkaline earth metal salts), resulting in a high level of environmental and hygienic safety for its use in both industrial and domestic settings.

[0033] 3. The new desiccant has the ability to quickly regenerate when dried under mild conditions (80 - 100 оC), in which the bentonite component almost completely restores its sorption capacity for the aqueous phase. Thus, the degree of sorption capacity restoration for Composition 3 and Composition 5 after 5 regeneration cycles is 96% and 90%, respectively, while for the closest analogue it is only 75%.

Claims

A granular moisture absorber based on natural layered aluminosilicates, including bentonite clay and a porous adsorbent, characterized in that the bentonite clay is granulated bentonite with a montmorillonite content of at least 85% by weight, a granule size of 1.5–4 mm and a moisture content of 2–6%, and the porous adsorbent is activated carbon and silica gel in the following ratio of components, % by weight: Bentonite clay 40 – 99 Activated carbon 0,5 – 60 Silica gel 0,5 – 60