CS199187B1 - Process for preparing aluminium oxide oxihydrate and/or active oxide as adhesive or catalyst carrier - Google Patents

Description

The invention relates to a process for the preparation of alumina and / or active oxide.

Hydrates, oxide hydrates and aluminum oxides in various forms are prepared with a view to their use as adsorbents, catalyst supports _x or even catalyst mass binders. In the latter case, it is usually necessary to peptize the prepared carrier mass to maintain sufficient mechanical strength after molding. It has now been found that the choice of a precipitant in the preparation of alumina from sodium aluminate solutions can affect the surface properties of the precipitated oxide hydrates so that after drying the prepared material can be extruded without or with very little peptization. porosity, which is important for the preparation of carbonated catalysts and for their high effective catalytic activity. Similarly, you can. to use such oxide hydrates as inert or other otherwise unformable binders, with the addition of a binder which then allows the preparation of a suitable mechanical strength, in addition again. with high porosity. In order to influence the surface properties, the precipitation takes advantage of the fact that the organic acids are sorbed onto the oxide hydrates by the OOH group and the remaining alkyl group hydrophobises the surface of the precipitated oxide hydrate. The stability of the resulting porous system can also be enhanced by the addition of surfactants when washing the oxide hydrate precipitate with water to remove foreign ions. The purity of the precipitated alumina was increased by filtering the aluminate solution through dried hydrates or active aluminum oxides, where, in addition to filtration separation, the solution was suspended. In the case of imported admixtures of SiO ₂ and Fe-oxides, ion exchange of dissolved impurities occurs.

Aluminum oxide and its oxide hydrates are among the most commonly used carriers and catalysts in the chemical industry. In the CSSR, where aluminum salts that are not suitable for the preparation of a suitable active mass by hydrolysis are industrially available, it is necessary to use sources of Al2O3 from the aluminum industry and to prepare sodium aluminate by dissolving in sodium hydroxide solution. This solution is then precipitated mostly with inorganic acids or salts capable of causing the hydrolysis of the alumina to produce the oxide hydrates for the production of the active alumina, which can be separated by filtration and washing. Nitric acid is the most commonly used, and to facilitate the process, it precipitates mostly at pH 7, leaving not only all non-99X87 purities contained in the original aluminate solution, but also a few percent of nitrate ions in order to remove it. elevated temperatures. In addition, the higher pH of precipitation strongly complicates the washing and the degree of alkali elution, so that the prepared support is usable only for a limited number of catalyst types and its usability also limits the content of Fe and SiO _{2 of the} order of 10 ² to 10 ^-1 wt%.

The precipitation of sodium aluminate with inorganic acids is commonly used for the preparation of oxide hydrates and has been extensively studied. All gels of the bohemic structure with high content of NO ₃ ions are formed. Its aging at higher temperatures and washing with ammonia solution results in aging and the formation of a more perfect bohemic structure. To prepare the binder, the prepared hydrates must be peptized with acid in a relatively high amount after drying. This achieves a high strength of the shaped particles, but almost without macropores. The volume of micropores changes little. A well peptisable hydrate and at the same time well dispersible to an aqueous suspension can be prepared by hydrolysis of Al-alcoholates. Representative alumina of this type is, for example, the alcoholate alumina produced as a by-product, used for the preparation of carriers containing only TiO ₂ as an impurity. The pore volume and size is influenced either by the addition of volatile or combustible substances, or, for example, during the washing process by the addition of ammonia to the washing water.

The preparation of easily peptisable alumina, preferably by water alone - by kneading with water to form a sol is therefore of utmost importance both for the preparation of shaped carriers with a bidispered porous structure and for the preparation of binders of other, poorly formable carriers and catalysts.

The above drawbacks have no method for the preparation of alumina oxides and / or no. The composition according to the invention is characterized in that the sodium aluminate solution with a concentration of 10 to 300 g Al ₂ O ₃ / l, preferably 100 to 250 g / l, Filtration through a layer of active alumina or active alumina precipitates at 20 to 80 °, preferably 50 to 60 ° C, and a pH of 6 to 9.5, preferably 8 to 9, at a volumetric rate of 1 hour ¹ , with an organic acid, preferably formic acid 1 to 10 N, preferably 4 to 8 N, and the prepared hydrate is separated from the mother liquors by filtration and washing, preferably by adding surfactants to the filter water and dried at a temperature of up to 180 ° C, optionally further processed by peptization with water or organic acid or nitric acid. The purity of the starting materials is critical to obtaining alumina oxides of satisfactory chemical purity. The purity of the raw materials for the preparation of sodium aluminate cannot be influenced and therefore the possibility of removing dissolved and suspended Fe and Si oxides by filtering the aluminate solution through a layer of active aluminum oxides or partially annealed was investigated. alumina hydrates. It has been found that at a flow rate of 1 liter of solution per liter of filter mass per hour, it reduces the content of said impurities from 10 ^-1 to 10 ^-2 to 10 ³ to 10 ^-2 , i.e. to values suitable for preparing low-concentration catalysts on supports, for example. type of alumina. The aluminate solution thus prepared or, if necessary, the unfiltered solution is precipitated at pH 6 to 9.5, preferably 8 to 9, and at a temperature of 20 to 80 ° C, preferably 50 to 60 ° C, with organic acids which are capable of forming oxides on the surface hydrophobic film. For operational reasons, it is used for the precipitation of aluminate solution containing 10-300 g A1 ₂ O _3/11 solution and the acid in a concentration of 2-10 N, preferably 4-6 N. The precipitated hydrates bohmitické structures are filtered with cold water, if appropriate with addition of surfactants, and dried at temperatures up to 180 ° C.

An advantage of the process according to the invention is that the prepared hydrate has such a secondary structure that it can be crushed by simple grinding to a very fine powder with a low bulk material which is easily peptized. Peptization can be carried out with both nitric acid and organic acids, which is again advantageous in terms of weakening the macropore.

Example

The effect of aluminate precipitation conditions with formic acid on the composition of the prepared oxide hydrates under constant washing of the precipitate with water is shown in Table 1.

Table 1

Precipitation of unfiltered sodium aluminate with formic acid.

pH precipitation wt. % C Na ₂ O Fe SiO ₂ 9.5 6.5 0,1-0,2 0.15 0.01 nesta- noveno 0,3-0,5 0.01 0.008 nesta- noveno 8.5 (operational, intensive washing) . 0.8 0.01 0.016 0.4

The results confirm the dependence. adsorption of the acid to the pH of the precipitation, as well as the ease of elution with the alkali from the precipitate. The content of other impurities is suitable for use of the prepared hydrate as a catalyst carrier with a higher concentration of active ingredients and as a binder. Therefore, in Table 2 we present the results of peptization of differently precipitated oxide hydrates.

Table 2

Péptization of precipitated oxide hydrates.

Φ strength 1 procedure of peptizing acid 4-> O «5 β r, w O> N g o & O β concentration of mass % water absorption% -P ·> £ X) 44 O oj tí 44 Λ i-4 4- » bulk density kneaded with water only 87 1.3 4.0 569 CH ₃ COOH 1 6 67 1.6 4.6 556 HCOOH 1 6 65 1.3 4.9 600 HNO ₃ 3 30 68 2.4 8.1 530 hno ₃ 3 30 105 1 0,5 1.6 390

1) starting oxide-hydrate prepared by precipitation of aluminate. operating at pH 8.5 · with HCOOH acid,

2) the starting oxide hydrate prepared by precipitation in the laboratory with formic acid at pH 8.5,

3) starting oxide hydrate prepared by precipitation of aluminate in the laboratory with nitric acid, at pH 8.5.

The results shown in Table 2 confirm the positive effect of organic acid precipitation on the strength and peptisability of the prepared oxhydrates. Even the extrudes prepared by mere kneading with water still have a satisfactory strength, while the same extrudates prepared by the strong peptization of oxides of hydrates prepared by nitric acid precipitation have a completely inadequate strength. Similar experience has been obtained using the hydrates as binders and for the preparation of water vapor catalysts. Nor should it be neglected that by annealing the oxide hydrates in the preparation of active alumina, adsorbed formic acid residues are more easily removed than nitric acid residues.

Claims (1)

Process for preparing alumina oxides and / or active alumina as a binder or catalyst support from sodium aluminate solution, characterized in that a sodium aluminate solution having a concentration of 10 to 300 g Al2 Og / l, preferably 100 to 250 g / l, is used. , optionally after filtration through a layer of active alumina or active alumina at a bulk rate It precipitates at 20 to 80 ° C and pH 6 to 9.5, preferably 8 to 9, for 1 hour ^-1 with an organic acid, preferably formic acid, at a concentration of 1 to 10N, preferably 4-8 N, and separates the prepared hydrate from the mother liquor. lyes, filtration and washing, preferably with the addition of surfactants to the filter water and dried, optionally further processed by peptization with water or an organic acid or nitric acid.