Process for the preparation of high purity aluminum alcoholates
SUBSTANCE: The process involves the pretreatment of aluminum compacts followed by their dissolution in lower alcohols and the purification of the resulting aluminum alcoholates. The pretreatment is by heat treatment until stable emissions in the metal matrix are formed, which are incoherent with the primary solid solution.
The invention relates to the preparation of organoaluminum compounds and the development of a process for the preparation of highly pure aluminum alkoxides, which are particularly widespread as precursors in the synthesis of functional ceramics.
Process for the preparation of a high purity aluminum alcoholate stated in the article: High ALCOHOLATE technology for the production of nanopowders and thin films. Greenberg, EE, SV Ivanov, Black NG and Physical Mesomechanics. 7. Special edition. Part 2, 2004, 69-72. The process consists in the recovery of aluminum alcoholate and its purification by vacuum distillation and rectification.
The method is implemented in a number of actions, namely:
- Dissolution of the aluminum compact in isopropyl alcohol;
- Vacuum distillation purification of aluminum isopropylate under pressure (0,1 to 3) mm Hg.St. and temperature (132-136) ° C;
- Rectification of aluminum isopropylate in the same way.
The content of impurities in the final product is not more than 10 ppm (0,001% of the mass.).
The disadvantages of this method are:
- Formation on the surface of the compact of aluminum, when it is dissolved, dense spatial lattice point relieving insoluble intermetallic compounds of silicon and elemental silicon, preventing the process of further dissolution of aluminum, which leads to a reduction in the rate of dissolution, and therefore performance the process in the end product - isopropylate aluminum;
- Contamination of the end product silicon, as it arises from the dissolution of the silicon alkoxide in the context of vacuum distillation, is a stable compound with a small separation factor in the system "liquid - vapor" common binary solutions. In addition, in the process of dissolving aluminum-alcohol elemental silicon hits isopropylate aluminum in the form of a fine aerosol, which is practically not removed by vacuum distillation and rectification.
Process for the production of a high-purity aluminum alcoholate (Patent RF 2278850, SS 31/32, Publ. 27.06.2006/2/3). The process is carried out by deleting aluminum alkoxides through the column at a certain temperature for several hours, filled extrudates γ - Al0,4O0,8 with a pore volume of 3 to 2 cm3 / G. The extrudates γ - Al1.6O3get a preview of the hydrolysis of aluminum alkoxides, obtained by molding aluminum hydroxide into extrudates with a diameter of 3 to 4 mm and a length (400-500) mm with subsequent calcination at a temperature (2-3) ° C . The γ - Al3O6 extrudates have a good adsorptive capacity, which makes it possible to partially capture the aerosol silicon present in the purified aluminum alcoholates that have previously been subjected to distillation or other purification in order to achieve a technologically acceptable degree of purity. This process enables you to create a technology for purifying aluminum alkoxides with a hydrocarbon chain length of C10 to p3 and, moreover, impurities from the specific to the individual element to an average value (10-4-10-1)% by weight. (XNUMX ppm - XNUMX ppm).
The disadvantages of this method are:
- poor quality of aluminum isopropylate, since compounds such as silicon in the purified product are only 40 to 80 ppm due to the good solubility of silicon alkoxides in the aluminum alkoxides;
- Complication of the hardware strapping process while lengthening the technological cycle of the production of purified aluminum isopropylate.
Process for the production of aluminum isopropylate of high purity, as described in the article: "A novel method for removing trace impurities silicon from aluminum tri - isopropoxide" Mingyan Wang, Gulling Ning, Jie Liu, Yuan Lin, Liu Yuguo // The National natural science foundation, No. 20376009. The method consists in the addition of lanthanide 1% of the mass, based on the aluminum contained in isopropylate aluminum, followed by boiling at a temperature (80 to 90) ° C for (7-8) hours.
The procedure is as follows: In anhydrous isopropyl alcohol, metallic aluminum is dissolved, then the reaction is carried out in boiling isopropyl alcohol at atmospheric pressure. It turns isopropylate-aluminum with impurities of organic silicon compounds (as authors of the article). In the process of dissolution of aluminum is added to a metal lanthanide ~ 1% of the mass. compared to aluminum. After addition of the lanthanide-matched metal-lanthanide organic silicon compounds, new silicon compounds with a high boiling point. While the synthesized isopropylate-aluminum is vacuum-distilled, the compounds of silicon-lanthanide remain in the distillation residue. After distillation, the amount of impurities in silicon in the isopropylate-aluminum was 2,6 ppm (0,00026 wt%).
The disadvantages of this method are:
- Increase in the time taken by the process of synthesis of aluminum isopropoxide due to the required 8-hour boiling of aluminum isopropoxide with the lanthanide, with a significant impact on the performance of the process;
The complexity of the process, as it is necessary to clearly track the concentration of lanthanide added to isopropyl aluminum. If the number of lanthanides is insufficient, uncoordinated organic silicon cannot be removed from aluminum isopropylate. On the other hand, if excess amounts of lanthanide castorena can form an unstable complex with the lanthanide, which is broken down into isopropylate of aluminum by vacuum distillation.
As a prototype, the process described in the Russian Federation No. 2395514, SS 31 / 32 27.07.2010 for the production of high purity aluminum alkoxide was published. The method consists in the interaction of aliphatic alcohol with 2 to 4 carbon atoms, activated alumina, whose purity is not inferior to 99,97%, with the subsequent purification of the resulting product. The process is as follows: load dissolved in a tubular reactor, the excess of aluminum activated with tin in the presence of ammonium halides. Alcohol is metered into the top of the reactor while the bottom of the reactor is heated to a temperature equal to the melting point of aluminum alcoholate. The resulting alkoxide cleans the simple vacuum distillation. The inventive technology allows for the synthesis of the product continuously with automatic delivery of activated alumina into the reactor as an output, and the need in this phase, such as the stripping of excess alcohol in the allocation of the target product, is eliminated. Aluminum alkoxides obtained by the proposed method according to atomic emission analysis, wherein the total content of impurities is not more than 1-10-3% by weight. (10 ppm). The production of aluminum alcoholate in relation to the alcohol composition contains 90%.
The disadvantages of the prototype are:
- Complexity of technology due to the introduction of an additional activator (tin) and a variation of the classical technology of synthesis;
- the content of impurities in the end product is 10 ppm (10-3% by mass), it is not enough to produce optically transparent ceramics from this product purity;
- the price of the product due to the additional time and energy costs.
The aim of the invention is to increase the purity of Aluminiumalkoholat while simplifying the technology.
Using the present invention results in the following technical result:
the silicon content in the final product does not exceed 0,01 ppm (10-6mass%);
- Increase in the productivity of the process by accelerating the dissolution process of the compact aluminum.
In order to solve the above problem and to obtain a technical effect in the method of producing high purity aluminum alkoxides involving pretreatment of the aluminum compacts and their subsequent dissolution in lower alcohols and purification of the resulting aluminum alcoholates, pretreatment of the aluminum compacts is accomplished according to the invention Heat treatment performed before the formation of the matrix metal-containing stable phases, in advance with their primary solid solution.
It is also possible:
- heat-treated compact aluminum components of the series Al - Mg - Si, which are carried out at a temperature (130-180) ° C for (10-30) hours;
- cleaning device by distillation;
in particular the purification of aluminum isopropylate under pressure (0,1 to 3) mm Hg.St. and temperature (132-136) ° C.
The dissolution of aluminum in alcohols provides an alcoholate of aluminum and ALCOHOLATES of impurities in a compact aluminum and the formation of insoluble aerosol impurities such as silicon. The formation on the surface of the compact of aluminum, when it is dissolved, dense spatial lattice point of the discharge of insoluble elemental silicon prevents further dissolution of aluminum, which leads to a decrease in the rate of dissolution, and therefore a decrease in the performance of the process in the end product - isopropylate aluminum . The physical basis of the effect - difficulty arising from the diffusion of alcohol vapors through a dense coherent lattice of a metal matrix point of the discharge of insoluble intermetallic compounds of silicon and elemental silicon to the surface of the dissolved metal (Article: Technology ALKOHOLATE high purity for the production of Nanopowders and thin layers. Greenberg, EE, SV Ivanov, Black NG and Physical Mesomechanics. 7. Special Edition. Part 2 (204) 69-72). The subsequent purification of the aluminum alcoholate by vacuum distillation reduces the amount of impurities, but the silicon content remains high and exceeds (5-10) ppm or (5-10-4-10-3)% by weight.
Introduction to the inventive method, a special heat treatment metal compact aluminum (before its dissolution in alcohols), focusing on training in the matrix metal discharge stable phases, incoherent with its primary solid solution, provides a number of technical effects. Namely, coagulation, for example, magnesium and silicon, and iron impurities in the aluminum pellets any source of purity, in large agglomerates with one hand. On the other hand, in the process of metal dissolution in alcohol the formation of such coagulants dramatically reduces the density of the lattice point (increased in the process special handling compacted aluminum) secretion practically insoluble phases are intermetallic compounds of silicon, elemental silicon and other metallic impurities ( eg Mg2Al3, Mg2Si, Si), Fe3SiAl12Fe2Si2Al9), which are deposited in the soil sediment in the Earth's gravitational field in the form of insoluble intermetallic inclusions and do not slow down the process of dissolution of aluminum and provide improved performance of the Alu-Alumi fusion process while the content of impurities of silicon is reduced to a level of not more than 0.1 ppm (10-5% by weight).
After the vacuum distillation, which is carried out, for example, by the method of the aluminum alcoholate described above, a higher purity of silicon results because the initial concentration of elemental silicon and its compounds in the starting material has been greatly reduced. The silicon content in the final product after vacuum distillation does not exceed 0,01 ppm (10-6 wt%).
Thus, holding a special heat treatment of the compact aluminum prior to its dissolution in alcohol offers the purification of aluminum alcoholate of silicon in the process of its synthesis, which ultimately gives such a severe technical effect as increasing the gap ratio of the silicon to the level of its content of no more as 0,01 ppm (10-6 wt%) in the process of its further purification according to a known method.
The implementation of the process for purifying aluminum alcoholate is illustrated by the following example.
Example 1.
Take a metal CD with technical grade aluminum brand AMg6. Its chemical composition: silicon, up to 0,5%, magnesium or 5,8%, aluminum 93,68%. Load it for 15 hours in a muffle furnace at a temperature of 150 ° C. Mechanical crushing of the CD to a particle size (10-20) mm, which is then solved by a special technology in every topilova alcohol.
After heat treatment of the compact of aluminum, silicon and magnesium and the associated impurities of the iron, there is no coherence with the matrix metal coagulants that are local (bright light on a dark background) as shown in Fig. 1 (Mg2Al3, Mg2Si , Si, Fe3SiAl12Fe2Si2Si2Al9). Under the influence of alcohol on the processed compact aluminum coagulants, the coagulants are practically insoluble and settle in the trays, which are subsequently removed from the system. The silicon content in the resulting alcoholate of aluminum does not exceed 0,1 ppm (0,00001 wt%). After the vacuum distillation according to paragraphs 3 and 4 of the invention, the impurity content of silicon is less than 0,01 ppm (0,000001% by weight), whereby the dissolution rate of aluminum in alcohol increases not less than 2,5 times.
Fig.1 and 2 show the microstructure and spectrum of the randomly selected coagulants of the compact aluminum brand AMg6 after the heat treatment according to paragraph 2 of the claims.
Implementation of the present invention reduces the cost of obtaining alcoholate from high purity aluminum due to the increase in productivity in the dissolution of compact aluminum; while the realization of the possibility of increasing the silicon content to not more than 10-6% m in a known manner purified isopropylate aluminum.
1. Process for the preparation of high purity aluminum alkoxides, consisting of the pretreatment of the aluminum compacts and their subsequent dissolution in lower alcohols and the purification of the resulting aluminum alkoxides, wherein the pretreatment of the aluminum compacts is carried out by heat treatment prior to the formation of the matrix metal-donating stable phases having their primary solid Solution incoherent.
2. A method according to claim 1, characterized in that the heat treatment of the aluminum of the compact series Al-Mg-Si is carried out at a temperature (130-180) ° C for (10-30) hours.
3. A method according to claim 1, characterized in that the purification is carried out by a distillation process.
4. Method according to claim 3, characterized in that the cleaning at a pressure (0,1 to 3) mm Hg.St. and a temperature (132-136) ° C is performed.
Translation of the Russian patent by the Institute for Rare Earths and Metals. We apologize for the German language used in this article, ultimately it's about the content.
