CS217824B1 - Process for preparing synthetic mordenite - Google Patents

Abstract

The invention relates to a method for preparing synthetic mordenite by hydrothermal treatment of a reaction mixture containing SiO-, AlO, and alkali, in which a telcut suspension J prepared by precipitation of sodium aluminate . silica sol or sodium water glass with the addition of acid is subjected to crystallization at temperatures of 100 to 220 ° C and a pressure of 0.1 to 5.0 MPa, optionally with the addition of crystalline mordenite from the previous batch, after which the crystalline mordenite is separated and further processed. Synthetic mordenite is suitable for adsorption and catalytic purposes.

Description

The invention relates to a method for preparing crystalline moroenite and consists in hydrothermal processing of a reaction mixture formed by precipitation of sodium aluminate or another aluminum compound together with silica sol or silica gel, or water glass.

The use of synthetic crystalline zeolites as molecular sieves and catalysts has recently found wide application. A number of processes for the preparation of synthetic mordenite-type zeolites have been developed, using various starting materials and operating conditions.

The various forms of mordenite reported in the literature are derivatives of the original sodium form after ion exchange. The chemical composition of mordenite is generally given as (Na ₂ O) ₄ . (AlgOj)^ · . (SiO ₂ ) _4Q . 24H ₂ 0.

Mordenites are silica-rich zeolites characterized by a micropore system composed mainly of parallel elliptical cylinders with a maximum diameter of 7 to 9 .

. 10' ⁸ cm, which are interconnected by narrow side channels.

Mordenites are characterized by high thermal stability and are more resistant to acids than, for example, Y-zeolites. About 80% (A1O ₄ ) of the tetrahedral form of Na-mordenite can be hydrolyzed by strong acid without significant loss of crystallinity. Decationated mordenites contain both Bronsted and Lewis acid centers.

Although mordenite occurs naturally as a mineral and can be modified and used for catalytic purposes by various processes, especially acid treatment, synthetic mordenite, characterized by high purity and crystalline form, is a suitable component for both adsorption and catalytic purposes and is used in various catalytic processes. Compared to various molecular sieve-based adsorbents, mordenite is characterized by a high molar ratio of SiO2/Al2O3.

As catalysts, mordenites can be used for isomerization of, for example, C8-aromatics or cyclohexane, for alkylation, disproportionation, dehydration, polymerization, and a number of other reactions.

SiO ₂ in the form of sodium silicates and silica gel is used as starting raw materials for the preparation of mordenite, thus obtaining the desired high SiO ₂ content in the starting mixture.

The composition of the starting mixture, working conditions and crystallization time have a significant influence on the formation and purity of mordenite. The formation of individual phases during crystallization is as follows:

amorphous SiO^-> phillipsite —'-»mordenite—->analcine

Analcine is the most stable crystalline phase.

At constant temperature and crystallization duration, a higher SiO/AlGO ratio in the starting mixture for the formation of mordenite requires a higher NaO/AlGO ratio.

At constant temperature, crystallization time and SiO ₂ /Al ₂ O^ ratio, the formation of analcine increases with increasing NaO/AlgO^ ratio, and conversely, with increasing SiOg/AlgO^ ratio at a constant Na ₂ /Al ₂ 0 ₃ ratio, the formation of mordenite increases.

If mordenite is to be obtained at a higher temperature, then the starting mixture for crystallization must have either a higher SiO 2 content or a lower Na 2 O 2 content.

According to the invention, it has been found that synthetic mordenite can be prepared under relatively mild operating conditions, i.e. temperature and pressure, if the starting reaction mixture is subjected to hydrothermal treatment with the addition of one or more anions of an inorganic or organic acid, or if the starting reaction mixture is seeded with mordenite crystallites from a previous production batch.

The essence of the method according to the invention lies in the fact that the starting reaction mixture prepared by reacting sodium aluminate or another aluminum compound with silica sol containing less than 1%

NagO or technical sodium water glass in a molar ratio of SiOg/AlgO^ of 5 to 40 and a molar ratio of NagO/SiO in the range of 0.1 to 0.5 and a molar ratio of HgO/NaO in the range of 10 to 250 at a pH of the reaction mixture of 7.5 to 12 with the addition of inorganic acids, such as H ₂ SO ₄ , HNO-j,

HCl, HF, and their ammonium salts or organic acids such as HCOOH,

CH^COOH, mixtures of C? to Cg fatty acids or olein, i.e. mixtures of fatty acids containing about 70% of oleic acid, sulfonated fatty acids, etc. and their ammonium salts are subjected to heat treatment at a temperature of 80 to 220 °C and a pressure of 0.1 to 5 MPa for 1 to 30 days, after which the reaction mixture is cooled, filtered and washed with either water, or diluted acid or NH^OH, or NH^NO^ or a mixture thereof, etc. to remove alkyls, thereby obtaining a product that is dried, formed and then heated alone or in a mixture with amorphous SiO2, or alumina with the addition of peptizing acid at a temperature of 100 to 750 °C.

The advantages of synthetic mordenite-type zeolites over natural ones lie in the constant composition and structure of mordenite, which do not undergo such variations as are the case with changing localities of natural mordenites.

The addition of inorganic or organic acids, or their ammonium salts, favorably influences the formation of mordenite crystals and facilitates the leaching of alkalies from mordenite.

It has long been found that easier crystallization can be achieved by seeding the initial reaction mixture with mordenite crystals, e.g. from a previous production batch, thereby shortening the time required for crystallization, obtaining a purer form of mordenite and allowing lower temperatures to be used during crystallization. The amount of crystalline mordenite, e.g. from a previous production batch added to the initial reaction mixture can range from 0.1 to 25 wt. %, based on the SiO2 contained in the reaction mixture.

However, powdered siloxide or hydrated SiO2 can also be used as starting materials for the preparation of mordenite, which, together with sodium aluminate or aluminum sulfate or aluminum chloride, after mutual precipitation at pH 7.5 to 12, is subjected to hydrothermal processing at a temperature of 0.00 to 220 °C and a pressure of 0.5 to 30 MPa with occasional stirring of the reaction mixture, which, with the addition of water, forms a thin liquid suspension.

The thermal treatment of the reaction mixture usually takes 1 to 5 days depending on the composition of the initial reaction mixture and the operating conditions used, whereby mordenite crystals of the desired form are formed. The reaction mixture is then cooled and the solid product is separated from the mother liquor, while the remaining mother liquor can be added to the initial reaction mixture after treatment. The obtained reaction product is washed with water or diluted acid or a mixture of acid and NH^OH, whereby the Na ⁺ content in the prepared mordenite is mainly reduced by ion exchange using a wide range of salts, or the desired catalytic metal substances such as Mo, W, Co, are introduced into the mordenite.

Ni, F, Β, P, etc. The obtained product is optionally washed again with water, dried, shaped and heat treated.

Mordenites prepared in this way can be in the form of powder, granules, extrudates, tablets, etc. However, they can be formed into the desired shape together with other materials, such as clay, bentonite, kaolin, diatomaceous earth, amorphous Si0 ₂ , silica sol, alumina, etc. after complete homogenization, or after peptization with acids.

These materials, such as alumina hydrogels, silica sols, silica gels, etc., act as catalyst binders and serve to increase the strength of the formed catalyst, but they can also significantly influence the properties, especially the activity and selectivity of the prepared mordenite as a catalyst. Mordenite, whether in the form of a wet hydrogel or dried powder, can also be combined with synthetic or natural aluminosilicates, powdered siloxides, SiO ₂ -TiO ₂ , AlgOyTiOg, etc., in various proportions ranging from 1 to 90% by weight. Synthetic crystalline mordenite can be added to natural mordenite that has been variously treated and treated with acids.

Mordenite can be formed either alone or after prior combination with catalytically active metal substances, which are introduced into the mordenite by saturation with salt solutions of these catalytically active components, or by ion exchange, in particular with compounds of molybdenum, tungsten, cobalt, nickel, platinum, chromium, palladium, copper, etc. However, it is possible to add mordenite in the form of hydrogel or powder after combination with catalytic substances to the filter cake or the pressed dried catalytic mass Co-Mo-AlgO^ or W-Ni-AlgO^ or Ni-Mo-AlgO^ etc., or to add crystalline mordenite during precipitation or to the precipitated suspensions of these catalytic masses and coprecipitate it with them, or to add mordenite after washing these catalytic masses from alkalis or during tableting or extrusion molding into the initial perfectly homogenized catalytic masses. The influence of working conditions, especially temperature and pressure during hydrothermal treatment of the reaction mixture on the formation of crystalline mordenite is relatively significant. For example, with the composition of the reaction mixture: NagO : AlgO^ : 15 SiOg : 150 HgO, the influence of the crystallization time was as follows:

temperature (°C) Pressure (MPa) crystallization time (h) CTG diffraction 170 1.0 10 amorphous SiOg 250 4.0 13 mordenite + analcine 190 20 amorphous SiOg + traces of mordenite 200 1.5 28 mordenite + traces of amorphous SiOg 280 5.5 4 mordenite + traces of amorphous SiOg 230 3.0 27 mordenite + amorphous SiOg 200 1.5 90 pure mordenite 190 1.4 69 mordenite + amorphous SiOg 175 1.0 95 pure mordenite

The values given in the table show that crystalline mordenite can be prepared from the reaction mixture of the above composition either by short-term crystallization within a few hours, but then it is necessary to use relatively high temperatures of 280 to 300 °C and pressures of 5.5 to 6.5 MPa, or under significantly milder working conditions, i.e. temperatures of 175 °C and pressures of around 1.0 SÍPa with an extended crystallization time of several days.

Crystallization of the reaction mixture, as already mentioned, can be carried out with the addition of inorganic or organic acids or their salts, e.g. water-soluble sodium or ammonium salts of propionic, mesic, valeric, caproic acid or mixtures of fatty acids up to C,g, etc. The addition of these fatty acids shortens the crystallization time, has an effect on the form of growing crystals, limits hydrolysis and caking of aluminosilicates on the reactor walls and has a beneficial effect on the filtration and washing of mordenite. These acids can be added either directly to individual solutions before precipitation or during precipitation or to the precipitated suspension. It is possible to add either only one acid, or more acids, or their mixtures in an amount of 0.1 to 25% by weight based on SiO2. However, sulfonated fatty acids, or sodium or ammonium salts of sulfonated fatty acids, alkylarylsulfonates, alkylethanolamine salts, etc., can be added to the reaction mixture.

Example 1

In 160 g of 40% NaOH, 68 g of hydrated alumina with a content of approximately 61% by weight AlgOj are dissolved, thereby forming a solution of sodium aluminate, which is mixed with 1,200 g of an aqueous solution of silica sol 30% containing 0.8% NaO. The resulting suspension is diluted with 100 ml of 25%

2.7824

HNO-j and thoroughly homogenized. The resulting liquid suspension having a pH of 1 is poured into a pressure vessel and heated to a temperature of 190 to 200 °C for about 90 h with frequent stirring. Then the reaction mixture is cooled, filtered and washed with distilled water and diluted nitric acid HNO-j. The washed product obtained is dried at .05 °C for 24 h. The white powder obtained in an amount of about 370 g shows pure mordenite according to X-ray analysis and has the following composition: 87 wt. %.

SiOg, 7% AlgO^ 1.2% NagO and 4.8% loss on annealing at 700°C.

Example 2 g of powdered hydrated alumina containing 61% AlgO^ ^{is dissolved in} 80 g of 40% NaOH and mixed with 1,500 g of technical sodium water glass containing 3. % by weight SiO^. 40 ml of 50% HNO^ is added to the resulting suspension and thoroughly homogenized. The resulting suspension has a pH of 11 and 5 g of filtered wet cake of mordenite crystals from the previous experiment 8. 1 are mixed in it and the suspension thus prepared is poured into a pressure vessel and heated to a temperature of 170 °C for 70 h. Then the reaction mixture is cooled, filtered and washed with water. The product obtained is dried for about 24 h and a white powder in an amount of about 230 g, which according to X-ray diffraction shows a crystalline structure of mordenite, has the following composition: SiO 83.5 wt. %, Na 2 O 5 wt. %, Al 2 O 4 wt. % and a loss on ignition of 8 wt. %.

Example 3 g of crystalline AlgíSO^)^ . 16HgO is dissolved in 80 ml of HgO and precipitated with 240 g of technical sodium water glass, resulting in a thin suspension having a pH of 9. This suspension is poured into a pressure vessel and heated to a temperature of 175 ° C for 90 h with occasional stirring. The reaction mixture is then cooled, filtered and washed with water and dilute nitric acid HNOj. The product dried at 105 ° C for 24 h shows pure mordenite in the amount of 70 g of powder according to X-ray analysis.

Example 4

In 80 g of 40% NaOH, 23 g of 61% powdered hydrated alumina are dissolved, thereby forming a solution of sodium aluminate, which is precipitated with a 30% aqueous solution of silica sol 1,200 g, and to the resulting suspension, 50 ml of 50% HNO^ and 20 ml of olein containing about 70% oleic acid are added. The suspension with a pH of 11 is heated in a pressure vessel at a temperature of 175 °C for 92 h, after which it is cooled, filtered and washed with water and NH^OH and HNOj. The product is then dried, according to X-ray diffraction it shows a crystalline mordenite structure of the following composition: SiO 85 wt. %, ^Al 2°3 wt. %, NagO 0.7 wt. %, KgG 0.03 wt. %, loss on ignition at 750 °C 9.5 wt. %.

Claims (2)

SUBJECT OF THE INVENTION A process for the preparation of a synthetic mordenite by hydrothermally treating a reaction mixture comprising SiO 2 / AlgO-j and an alkali, characterized in that the liquid suspension is prepared by precipitating sodium aluminate or other aluminum compound with silica containing less than 0.1% NagO or sodium water with SiOg / molar AlgO 5 to 40 and a molar ratio of NagO / SiO 2 of 0.1 to 0.5 and a molar ratio of H 2 O / NagO of 0 to 250 are added at an pH of the reaction mixture of 7.5 to 12 with the addition of an inorganic acid, e.g. PO 2, HF, H 2 BO 3 and their ammonium salts, or organic acids, e.g., sulfonated fatty acids and their ammonium salts, in an amount of 0.1 to 25% by weight, based on SiO 2, subjected to crystallization at 80 to 220 ° C at a pressure of 0.1 to 5.0 MPa, whereupon the crystalline mordenite formed is filtered off from the mother liquor, washed from alkalis and dried, and forms the cell, alone or in admixture with amorphous SiO2, or an aluoin from the peptizing addition. and then heat treated at 100 to 750 ° C. 2. A process according to claim 1, wherein from about 0.1% to about 25% by weight of the starting reaction mixture is added to the starting reaction mixture. crystalline mordenite from previous production