RU2283279C1 - Method of preparing granulated synthetic zeolites - Google Patents

Abstract

FIELD: zeolites.

SUBSTANCE: invention relates to methods of preparing granulated synthetic zeolites employed as adsorbents in drying processes and gas/liquid separation processes in petroleum processing., chemical and gas industries as well as in other areas. Calcined zeolite NaA or NaX granules molded with any type of natural binding material are treated with mother liquor previously formed in crystallization of powdered NaA or NaX-type zeolite converted into granules. Treatment is carried out for 2-6 h at 60-95°C and ratio of volume of mother liquor to mass of granules being treated equal to (1.5-6.0):1.0. Treated granules are washed with water from excess of sodium hydroxide and calcined once more at 300-550°C for 2 to 24 h. Invention allows characteristics of quality of granulated NaA or NaX zeolites to be improved by 2.5-3.0 times in what concerns mechanical crush strength and by 5-40% in what concerns dynamic adsorption capacity.

EFFECT: improved performance characteristics of granules, reduced dusting, and solved environmental problem with disposal of crystallization mother liquors.

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Description

The present invention relates to methods for producing granular synthetic zeolites used as adsorbents in the processes of drying, purification, separation of gases and liquids in the oil refining, chemical, gas and other industries.

The well-known "Method for producing granular synthetic zeolites" (AS USSR No. 210104, class B 01 J 12, 11/40, BI No. 6, 1968), according to which powders of kaolin and zeolite type A are mixed, moreover, the zeolite is taken in an amount of not less than 10 wt.%, counting on kaolin (preferably the introduction of zeolite in an amount of 25-70 wt.%). The mixture is dosed moistened and formed into granules. The obtained granules are dried, then calcined at 600-650 ° C for 6-12 hours. The calcined granules are placed in an alkaline solution and crystallized sequentially at 60 ° C for 24 hours, then at 95 ° C for 24 hours. Zeolite granules are washed with water from excess sodium hydroxide to a pH of 10.5-11.0 and dried.

This method has the following disadvantages:

1. The possibility of obtaining only granular zeolite type A, the formation of which occurs due to the crystallization of calcined kaolin (metakaolin) contained in the granules.

2. The need to use only kaolin powder as a binder additive to the zeolite powder.

3. A significant duration of crystallization (alkaline processing) of the granules.

A known method for producing type A zeolite, comprising mixing a solution of sodium silicate with aluminum hydroxide, with a suspension of kaolin and sulfuric acid. The obtained sol is fed into a molding column with oil, where a ball alumina-silica gel is obtained, which is subjected to syneresis in a transport fluid for 12-24 hours, treatment with a solution of ammonium nitrate and a solution of aluminum sulfate, washing, drying, calcining at 600 ° C for 8 hours, hydrothermal crystallization in an alkaline aluminate solution at 100 ° C for 24 hours, washing with water and drying at 100-120 ° C (A.S. USSR No. 1450272 A1, class C 01 B 39/00, 1987). The disadvantage of this method is the complexity of the technology for producing zeolite and the low quality of the final product. The specified method did not find industrial application.

A known method for producing type A zeolite, which involves mixing aluminosilicate material with aluminosilicon hydrogel, granulating, drying, hydrothermal crystallization in three stages in an alkaline aluminate solution, the temperature of the crystallization solution being 30 ° C in the first stage and the granules are kept at this temperature for 18 h, at the second stage - 60 ° С and 12 h and at the third - 85 ° С and 10 h, respectively. Next, the zeolite granules are separated, washed with water from alkali and dried (patent RU No. 2033967 C1, CL 01 39/20, 1992). This method allows to obtain type A zeolite with a content of zeolite material of 96-97 wt.%.

However, the main quality indicators of type A zeolite obtained by this method are relatively low, in particular, indicators of dynamic adsorption moisture capacity and flow rate of granules are low.

At the same time, the dusting rate of granules is unacceptably high, and the entire technology for the preparation of type A zeolite is complex and multi-stage.

The closest in technical essence and the achieved result to the alleged invention is the "Method for producing granular synthetic zeolites" (AS USSR No. 5222133, CL 01 33/26, BI No. 27, 1976), which selected for the prototype.

According to the prototype, powdered zeolite is mixed with a natural binder of materials, which use kaolinite or hydromica with a particle size of 250-500 ° A.

Powdered zeolite in sodium form is preliminarily prepared by a traditional method, according to which solutions of sodium silicate and aluminate taken in calculated ratios are mixed. The mixture is subjected to hydrothermal crystallization, resulting in a suspension of zeolite in the mother liquor. The zeolite is separated from the mother liquor by filtration, washed from excess alkali with water and dried. The ratio - the mass of the formed powdery zeolite NaA or NaX to the volume of the mother liquor is 1.0: 4.0 ÷ 6.0 depending on the composition of the initial reaction mixture.

The concentration of the mother liquor discharged into the waste:

- from zeolite NaX 0-20 g / l on SiO ₂ ; 50-110 g / l NaOH;

- from zeolite NaA 0-30 g / l according to Al ₂ O ₃ ; 50-110 g / l NaOH.

A mixture of powdered zeolite and natural binder is moistened and granulated.

The formed granules are dried to a residual moisture content of 20-25% at 150-200 ° C and calcined at 600-700 ° C for 16-24 hours. The calcined granules are cooled and treated with 1-10% sodium hydroxide solution at 75-90 ° C and constant stirring. The granules are washed from excess alkali (caustic soda) with water and re-calcined at 350-450 ° C for 4-24 hours.

Granular zeolites subjected to alkaline treatment have an increased dynamic capacity for pairs of molecules adsorbed by them.

This method has the following disadvantages:

1. The need to use a solution of caustic soda, and a certain concentration, which is associated with additional costs for raw materials and reagents to obtain granular zeolites.

2. Reduced mechanical strength and high dust formation of granular zeolites after treatment with sodium hydroxide.

3. The use of powdered zeolites for the preparation of granular zeolites requires preliminary separation of the mother liquor from the powdered zeolites, washing and drying. At the same time, 5-10 wt.% Of silicon oxide or alumina (depending on the type of crystallized zeolite like NaX or NaA) and 65-70 wt.% Caustic soda, based on the feedstock, are discharged into the waste water with the mother liquor and washings.

4. The mother liquor (pH 13-14), falling into water bodies and rivers, has an environmentally harmful effect on the environment.

The aim of the invention is to: increase the mechanical strength and dynamic capacity of the zeolite, reduce the dusting of granules, as well as reduce the harmful effects on the environment (environmental improvement).

This goal is achieved in that the calcined granules are treated with a mother liquor - stock formed during the synthesis of powdered zeolites of the NaX or NaA type, for 2-6 hours at a temperature of 60-95 ° C and the ratio is the volume of the mother liquor: the mass of processed granules is 1 5 ÷ 6.0: 1.0, washed from excess sodium hydroxide and re-calcined.

A comparative analysis of the proposed method with the prototype allows us to conclude that the claimed method differs from the known processing of granules with a mother liquor formed during the synthesis of zeolites such as NaX or NaA. Specifically, a sodium hydroxide solution is not prepared, and in the process of obtaining granular zeolites, the mother liquors formed during the synthesis of powdered zeolites that were previously dumped into the waste are disposed of. In addition, to obtain granular zeolites, their treatment with a mother liquor is carried out at 60-95 ° C for 2-6 hours and the ratio of the volume of solution: mass of granules equal to 1.5 ÷ 6.0: 1.0.

The specified technique allows us to conclude that the claimed technical solution meets the criterion of "novelty."

An analysis of known methods for producing granular zeolites showed that to increase the dynamic adsorption capacity of the zeolite, the method of alkaline treatment of zeolite-containing granules with a sodium hydroxide solution was previously known.

However, only the fact of processing granular zeolites of the NaA or NaX types formed with a natural binder material, a mother liquor formed during the synthesis of powdered zeolite of the NaA or NaX type at a temperature of 60-95 ° C for 2-6 hours and the ratio of the volume of solution: mass of granules equal to 1.5 ÷ 6.0: 1.0, allows to achieve an increase in mechanical strength and dynamic adsorption capacity of granular zeolite, to reduce the dusting of granules and to improve the environment due to the disposal of harmful effluents.

Thus, the authors first proposed the conditions for treating granular zeolites of the NaA or NaX types with a mother liquor from crystallization of the powdered zeolite NaA or NaX, which opened up the possibility of not only disposing of the mother liquors, but also made it possible to significantly improve the quality indicators of granular zeolites.

The essence of the invention is as follows. The calcined granules of zeolite NaA or NaX, formed with a natural binder of any type, are treated with a mother liquor previously formed by crystallization of a powdered zeolite of the NaA type introduced into the granular product. The composition of the mother liquor depends on the ratio of the crystal-forming components in the reaction mixture for the synthesis of powdered zeolite of the NaA type and is determined by the following concentration limits: Al ₂ O ₃ 0-30 g / l; NaOH - 50-110 g / l. In addition to the mother liquor from a zeolite of the NaA type, the treatment can be carried out with a mother liquor previously formed by crystallization of a powdered zeolite of the NaX type. The composition of the mother liquor from a NaX type zeolite depends on the ratio of the crystal-forming components in the reaction mixture for the synthesis of a NaX type zeolite powder and is determined by the following concentration limits: Si ₂ O 0-20 g / l; NaOH 50-110 g / l. The treatment is carried out for 2-6 hours at 60-95 ° C and the ratio of the volume of the mother liquor: the mass of the processed granules equal to 1.5 ÷ 6.0: 1.0. After processing, the solution is drained, the granules are washed with water from excess sodium hydroxide and re-calcined at a temperature of 300-350 ° C for 2-24 hours

The result is a granular zeolite of the type NaA or NaX having:

- 2.5-3.0 times higher mechanical crushing strength;

- 5-40% higher dynamic capacity;

- less dusting of granules.

The decrease in processing temperature below 60 ° C leads to a deterioration of both the adsorption and strength characteristics of the obtained granular zeolite.

Increasing the processing temperature above 95 ° C is not economically feasible due to the additional energy consumption and the need to use (at temperatures above 100 ° C) special autoclave equipment, usually not used in the synthesis of zeolites, which greatly complicates and increases the cost of the process.

The decrease in the ratio of the volume of the mother liquor: the mass of the processed granules below 1.5: 1.0 leads to a deterioration in both the adsorption and strength characteristics of the granulated zeolite.

An increase in the ratio of the volume of the mother liquor: the mass of the processed granules above 6.0: 1.0 is not economically feasible, because, on the one hand, it reduces the productivity of the process for producing granulated zeolite, and, on the other hand, with a ratio of 6.0 : 1.0, there is a complete utilization of the mother liquor formed during the synthesis of powdered zeolites such as NaA or NaX.

Reducing the processing time of less than 2 hours leads to a decrease in the efficiency of the interaction of the mother liquor with granular zeolite and, as a result, to a deterioration in the quality of the processed product.

An increase in processing time in excess of 6 hours is possible, but not technologically advanced due to a decrease in the yield of finished products.

The proposed method for producing granular synthetic zeolites is tested in laboratory and pilot conditions.

Example No. 1.

1 m ³ sodium silicate solution with a concentration of SiO ₂ = 100 g / l; NaOH = 46 g / l is mixed with 0.313 m ^{3 of a} solution of sodium aluminate with a concentration of Al ₂ O ₃ = 272 g / l; NaOH = 396 g / l. The ratio of SiO ₂ : Al ₂ O ₃ in the reaction mixture is 2.0. The mixture is crystallized at 95 ° C for 0.5 hours. A suspension of type A zeolite is obtained in the mother liquor with a concentration of: NaA zeolite = 180 g / l; NaOH = 80 g / l; Al ₂ O ₃ = 3 g / l. The zeolite is filtered off from the mother liquor and washed from excess sodium hydroxide with water. The ratio of the mass of zeolite NaA (counting on absolutely dry substance): the volume of the mother liquor is 1.0: 5.5.

All the resulting zeolite is mixed with 44 kg of natural binder - kaolinite clay with a particle size of 250-500 ° A, the resulting mixture is moistened and molded in the form of granules. The obtained granules are dried at 150 ° C to a residual moisture content of 20-25% and calcined at 650 ° C for 8 hours

The calcined granules are treated with a mother liquor - a drain previously formed during crystallization of powdered NaA zeolite for 6 hours at 60 ° C and a ratio of the volume of the mother liquor: the mass of the processed granules is 5.0: 1.0.

The treated granules are washed from excess sodium hydroxide with water and re-calcined at 550 ° C for 8 hours.

Get a NaA zeolite with a binder, having a crushing strength of 1.5 kg / mm ² , a dynamic capacity for water vapor of 122 mg / cm ³ and reduced dust formation of granules (85% wt.). The estimation of the amount of dust formation is carried out as follows. A sample (200 g) of granular zeolite with a diameter of granules of 3.0 mm is poured into 300 ml of water and stirred with air for 0.5 h, after which 800 μm granules are separated from the water on a sieve and the mass fraction of dry matter is determined in water. The mass fraction of dry matter in the wash water from the granular zeolite obtained by the prototype is taken as 100%.

The results of the remaining experiments and the data of the prototype are shown in table 1.

The implementation of the invention will allow 2.5-3.0 times to increase the mechanical crushing strength and 5-40% to improve the dynamic adsorption capacity while reducing dusting of granular zeolite. The replacement of the sodium hydroxide solution with mother liquors from the synthesis of powdered zeolites is associated with the utilization of these solutions and, consequently, an improvement in the ecology of the environment with a decrease in the consumption of sodium hydroxide in the production of zeolites.

Table
Preparation conditions and quality of the obtained granular zeolites No. of examples The solution used for processing, g / l Processing conditions The quality of granular zeolites NaOH SiO ₂ Al ₂ O ₃ Temperature ° C Time h Ratio, w: t Zeolite type The diameter of the granule, mm Crushing strength, kg / mm ² Dynamic adsorption capacity, mg / cm ³ Dust formation, wt.% water benzene one 2 3 four 5 6 7 8 9 10 eleven 12 13 According to the prototype 10-100 - - 75-95 2-8 - Nax 2.5-2.8 0.65-0.68 145-147 70 one hundred 10-100 - - 75-95 2-8 - NaA 2.7 0.37 88 - one hundred one 80 - 3 60 6 5.0: 1.0 NaA 3.0 1,50 122 - 83 2 80 5 - 80 four 4.0: 1.0 Nax 2,5 1.10 150 77 80 3 110 - thirty 60 2 1.5: 1.0 NaA 2.0 1.40 142 - 75 Continuation of table 1 one 2 3 four 5 6 7 8 9 10 eleven 12 13 four fifty - 2 95 3 6.0: 1.0 NaA 3.2 1.20 116 - 90 5 110 twenty - 60 2 3.0: 1.0 Nax 3.0 1.20 135 72 72 6 80 - 5 80 four 4.0: 1.0 Nax 2,5 1.30 155 82 87 7 fifty 3 - 95 12 3.0: 1.0 NaA 2.0 1.45 138 - 82 8 fifty - 2 fifty 3 6.0: 1.0 NaA 3.2 0.70 105 - 98 9 fifty - 2 95 3 1.0: 1.0 NaA 3.2 0.80 107 - one hundred 10 fifty - 2 95 one 6.0: 1.0 NaA 3.2 0.68 104 - 97

Claims (1)

A method of producing granulated synthetic zeolites by mixing powdered zeolite with a natural binder, moistening the resulting mixture, forming granules from the obtained paste, drying and calcining, characterized in that the calcined granules are treated with a mother liquor - stock, previously formed by crystallization of powdered zeolite NaA or NaX for 2-6 hours at a temperature of 60-95 ° C and the ratio of the volume of the mother liquor to the mass of the processed granules equal to 1.5 ÷ 6.0: 1.0, washed from excess sodium hydroxide and To Re-ignited.