Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/20—Silicates
  • C01B33/32—Alkali metal silicates

Definitions

• the invention relates to a process for the production of alkali metal silicates from crystalline SiO 2 -containing material and aqueous alkali metal hydroxide solution at elevated temperature and normal pressure.
• Alkali metal silicates e.g. Water glasses are produced in large quantities and used in many areas both in solution and as a solid. These include detergents and cleaning agents, adhesives, paints, ore flotation and water treatment. They also serve as raw materials for the production of zeolites and silicas, sols and gels (Büchner et al. "Industrial Inorganic Chemistry", Verlag Chemie, 1984, p. 333).
• Water glass solutions are customarily characterized by two physical sizes. On the one hand by the molar ratio Si ⁇ 2 / M2 ⁇ , called module below, and the solids content, i.e. the proportion by weight of SiO 2 and M2O in the solution, where M stands for Na or K. Both factors influence the viscosity of the alkali metal silicate solution.
• the maximum solubility of an alkali metal silicate with a specific module can be determined from tables and diagrams. In general, higher solids contents in the solution can be achieved at higher alkali contents, ie a lower modulus.
• Water glasses up to a module of 4.3 are obtained via melting processes. Such melting processes have been known for the past century; only the implementation of is common today Quartz sand with soda at temperatures around 1500 ° C (Winnacker-Küchler, "Chemical Technology", C. Hanser Verlag, 4th edition (1983), Volume 3, "Inorganic Technology II", page 58 ff). Only a small part of the alkali metal silicates represented in this way is sold as solid glass. The main amount is then dissolved in water. In the case of glasses with a modulus> 2.0, the reaction rate at the reflux temperature of the solution is unsatisfactory, so that pressure digestion at 4-6 bar and 150 ° C. is preferred.
• alkali-rich water glasses can also be produced hydrothermally from quartz sand and concentrated aqueous sodium hydroxide solution. Because of the low reactivity of the quartz sand, elevated temperatures and increased pressure are necessary for this. Technically, two processes are used: nickel-plated rotating pressure solvents at temperatures from 200 to 220 ° C and tube reactors at temperatures from 250 to 260 ° C (Winnacker-kuchler, op. Cit., Page 61 f).
• Finely distributed, amorphous silicas dissolve exothermically in alkalis.
• particularly pure alkali metal silicate solutions are sometimes obtained by reacting pyrogenic or precipitated silica with alkali alkali. Apart from special cases, this procedure is too expensive.
• Amorphous silica is also obtained as a by-product or waste in various technical processes. Several processes for the use of such silicas have been described.
• middle-modular sodium silicate solutions can be obtained from the waste silica of the AIF3 and HF production.
• dust from the production of ferrosilicon contains approx. 90% by weight of highly reactive SiO2, which is mixed with 8.1% sodium hydroxide solution at temperatures around 90 ° C to form a water glass Solution with a high module can be implemented.
• Na2Si ⁇ 2 solid, crystalline, anhydrous sodium polysilicate
• This sodium silicate of the gross composition Na2Si ⁇ 3 contains infinite chains of SiOj tetrahedra which are linked by bridges to the sodium atoms.
• Such chain silicates are referred to in mineralogy as “inosilicates” and in chemistry as “polysilicates”.
• the term "metasilicate” is also widespread but incorrect. In the following, the term “sodium polysilicate” is used exclusively.
• anhydrous sodium polysilicate is produced by an annealing reaction of quartz sand and soda in a rotary kiln at approx. 950 ° C (Büchner et al. "Industrial inorganic chemistry", Verlag Chemie, 1984, p. 333). The reaction time is about 45 minutes. At an even higher temperature, but then shorter reaction times, the polysilicate can also be obtained by melting sand and soda (Ullmann's Encyklopadie der Technische Chemie, Verlag Chemie, 1982, Vol. 21, p. 412).
• US Pat. No. 3,532,458 describes the hydrothermal production of sodium polysilicate starting from quartz sand. For a complete reaction of the quartz sand with an aqueous sodium hydroxide solution, temperatures of approximately 200 ° C. at elevated pressure are necessary.
• DE-AS 1567 572 proposes to produce anhydrous, crystalline alkali metal silicates, preferably sodium polysilicate, by using finely divided, solid alkali metal silicate which is heated to a temperature of above 130 ° C.
• Spraying an aqueous alkali metal silicate solution produces a film, and by means of an additional hot gas stream causes the water to evaporate, the coating and drying step being repeated until the size of the crystalline anhydrous alkali metal silicate particles has increased to the desired extent.
• part of the largely anhydrous alkali metal silicate is returned to the continuous process as a starting component.
• NL-OS 7802697 it is also known to produce sodium silicate solutions by passing sand with sodium hydroxide solution at elevated pressure and a temperature of at least 200 ° C. through a pipe which can be used for the continuous digestion of bauxite and, for example, from the DE-OS 21 06 198 and DE-0S 25 14 339 is known.
• the manufacture of metasilicate products is preferably carried out at a temperature of 200 to 240 ° C; For the production of products with a higher ratio of SiO 2 : Na 2 (), temperatures of 240 to 280 ° C are preferably used.
• the pressure in the tube is preferably in the range between 10,000 and 20,000 kPa. According to the method described in this laid-open publication, however, only solutions and no solid products are produced.
• DE-OS 31 24 893 describes a process for the production of water-free sodium polysilicate by treating quartz sand and / or quartz powder with concentrated aqueous sodium hydroxide solution under pressure at a temperature in the range from 200 to 400 ° C.
• R0 75620 (Chemical Abstracts 100: 24023u) describes a process for the production of crystalline sodium polysilicate with a module of 1: 1 from waste containing silicon dioxide from the production of fertilizers. This process is characterized in that the solution containing sodium polysilicate must first be filtered in order to remove impurities before the Filtrate is concentrated. The crystallization then takes place when the solution is cooled to a temperature of 10 to 15 ° C.
• SU-434060 (Chemical Abstracts 82: 45938w) describes a process for the production of sodium polysilicate from volcanic ash.
• JP-73/16438 (Chemical Abstracts 80: 17050r) describes a process for the production of solutions containing sodium polysilicate from flue gas residues.
• the object was achieved according to the invention by a process for the production of alkali metal silicates from crystalline material containing SiO 2 and aqueous alkali metal hydroxide solution at elevated temperature and normal pressure, characterized in that cristobalite and / or tempered quartz sand were used as the crystalline material containing SiO 2 uses and this material with aqueous, 20 to 50 wt .-% sodium or potassium hydroxide solution at temperatures in the range of 100 to 150 ° C and under normal pressure, the molar ratio of Si ⁇ 2 to Na2 ⁇ or K2O in the reaction mixture is in the range from 2: 1 to 1: 7.
• tridymite optionally together with amorphous silicon dioxide, can also be used for the process according to the invention, which likewise has a higher reactivity because of its structure, which is more open than that of quartz. Tempered quartz sands behave similarly, i.e.
• Quartz sands which have been annealed above 1000 ° C, preferably at 1300 to 1600 ° C, with the addition of catalytic amounts of alkali and which are composed of cristobalite, tridymite and optionally amorphous silicon dioxide.
• quartz sand By tempering quartz sand, as described in the unpublished German patent application P 3938 730.5, reactive SiO 2 phases are obtained which are composed, inter alia, of cristobalite, tridymite and amorphous SiO 2.
• the subject of this patent application is a process for the production of reactive silicon dioxide phases, which is characterized in that quartz sand is mixed with an alkali metal compound or its aqueous solution, the alkali metal compound being selected from the group of compounds which are used in Heating into the corresponding alkali metal oxides, that the molar ratio of SiO 2 to alkali metal oxide is between 1: 0.0025 and 1: 0.1 and that this mixture is heated to a temperature between 1100 ° C. and 1700 ° C.
• the tempered quartz sands are obtained from slightly contaminated starting compounds, ie quartz sands as are also used for the production of water glass in the melting process. This has the advantage that no additional residues occur during the working up, that is to say, if appropriate, the filtration of the alkali metal silicate solutions, and therefore an already mature technology can be used. This is in contrast to the problematic processing of the alkali metal silicate solutions, which are obtained from waste silicas and have already been discussed.
• the aqueous sodium or potassium hydroxide solutions used for digestion have a concentration of 20 to 50% by weight, for NaOH in particular a concentration of 40 to 50% by weight, in particular 50% by weight of sodium hydroxide, which corresponds to the technically available product corresponds.
• concentration of the potassium hydroxide solution is preferably 40 to 50% by weight, in particular 47 to 50% by weight.
• the tempered quartz sands are reacted with aqueous sodium hydroxide or potassium hydroxide at the boiling point of the respective alkali or the resulting alkali metal silicate solution or suspension (cf. Examples, Table 1).
• the boiling temperature is between 150 and 100 ° C and is not constant since the salinity changes during the course of the reaction.
• cristobalite was used as the SiO 2 source.
• the particle size was generally 0.1 to 0.8 mm.
• the process according to the invention can be carried out batchwise or continuously and is suitable depending on the process from the SiO 2 / alkali metal oxide module used to produce alkali metal silicate suspensions or solutions.
• suspensions of sodium polysilicate result in the module range SiO 2: Na 2 O of 1.2: 1 to 1: 2, preferably 1: 1; ie the sodium polysilicate is obtained as a solid, crystalline phase.
• SiO 2: Na 2 O of 2: 1 amorphous sodium silicates are formed, which are also obtained in solid form, ie as a suspension.
• the crystalline material containing SiO 2 is reacted with aqueous sodium hydroxide solution, the molar ratio of SiO 2 to Na 2 O in the reaction mixture being in the range from 1.2: 1 to 1: 2, preferably of 1: 1.
• the crystalline SiO 2 -containing material is reacted with aqueous sodium hydroxide solution, the molar ratio of SiO 2 to Na 2 O in the reaction mixture being 2: 1.
• Table 2 shows the times depending on the module used and the concentration of the alkali metal hydroxide reproduced, which were necessary for the complete dissolution of the SiO 2 used.
• the process is advantageously carried out at the boiling point of the aqueous alkali metal hydroxide solution or the resulting solution Alkali metal silicate solution or suspension performed.
• Lower temperatures slow down the reaction. Higher temperatures would increase the reaction rate, but they require increased pressure and therefore pressure vessels, which make such a process less economical.
• normal pressure in connection with the method according to the invention, this is understood to mean the usual ambient pressure of approximately 1 bar. In other words, this means that in the sense of the present invention, work is carried out without increased pressure.
• the sodium silicate suspensions obtained can be diluted by adding water until the solubility of the alkali metal silicates is below.
• the process according to the invention for the production of sodium polysilicates is demonstrated by means of further examples (Table 4).
• the process is carried out in the temperature range from 100 ° to 150 ° C. at normal pressure.
• the process according to the invention can be carried out in an open reaction vessel, since the high salt content of the reaction mixture causes the boiling point of the aqueous reaction mixture to shift towards higher temperatures.
• a sodium polysil cat in the reaction of cristobalite with aqueous 50% by weight sodium hydroxide solution in a molecular ratio of SiÜ2 'Na2 ⁇ of 1: 1 at an initial temperature of about 150 ° C and at normal pressure (1 bar) after a reaction time of 2 hours a sodium polysil cat can be obtained which contains water-insoluble residues of only 0.015% by weight.
• cristobalite or tempered quartz sand, ie cristobalite, trydimite and amorphous silicon dioxide was reacted with the stated amounts of aqueous alkali to carry out the process. The reactions were carried out in a glass flask at normal pressure.
• the temperature is still 70 to 130 ° C, preferably 90 to 110 ° C, warm Filter the suspension through a suction filter. A concentration or cooling of the reaction solution to initiate or improve the crystallization is not necessary in the process according to the invention.
• the filtrate (mother liquor) obtained during the filtration is preferably returned to the process after concentration.
• the sodium polysilicate remaining as a filter residue is usually still crushed warm (at 70 to 90 ° C) and then dried under reduced pressure (1333 Pa to 26664 Pa) under elevated temperature (100 to 150 ° C) to anhydrous sodium polysilicate .
• the drying time can be between 5 and 15 hours.
• the “anhydrous sodium polysilicate” obtained with the process according to the invention is understood to mean a sodium polysilicate which contains on average not more than 5% by weight and preferably less than 3.5% by weight of water. The water content was determined by determining the loss on ignition when heated to 1000 ° C. Only crystalline anhydrous sodium polysilicate can be seen in X-ray diffraction diagrams (comparison with JCPDS file No. 16-818). The suspensions of amorphous sodium silicate obtained with a module SiO 2 • Na 2 O of 2: 1 can also be worked up in the same way.
• Example 25 the reaction suspension was heated to the boiling point at atmospheric pressure. The boiling point decreased with the course of the reaction since the sodium hydroxide reacted.
• Example 27 the suspension was kept at a temperature of 100 ° C. This temperature is not sufficient for a complete reaction within 2 hours.
• Example 28 shows that a tempered quartz sand consisting of cristobalite, tridymite and amorphous silicon dioxide has the same reactivity as cristobalite.
• the aqueous alkali metal hydroxide solution (for example 50% by weight of NaOH, technical or 47% by weight of KOH, technical or solutions correspondingly diluted with water) was introduced and heated to boiling. The weighed amount of cristobalite was then added. The Siedetempe ⁇ temperature took mi 't the course of the reaction, since the Al used kalimetall liquor etallsilicat to the alkali (eg sodium silicate) react. The reaction time was 30 to 350 minutes, preferably 30 to 210 minutes.
• Table 1 The batch ratios for the individual experiments 1 to 24 (1 to 21 with NaOH; 22 to 24 with KOH) are shown in Table 1.
• Table 2 shows the reaction parameters of these experiments.
• Table 3 contains values for corresponding comparative examples in which quartz or quartz powder was used as the SiO 2 source instead of cristobalite.
• Quartz flour 1: 1 50 360 0.62 62
• A Three-necked flask with paddle stirrer, thermometer and reflux cooler, patio heater.
• B Analog A, but heatable with an oil bath.
• Experiments 25 to 27 relate to reactions with cristobalite
• experiment 28 relates to the reaction of tempered quartz sand (1400 ° C., 5% by weight * NaOH addition), consisting of cristobalite, tridymite, amorphous silicon dioxide and small amounts of sodium silicate.
• the loss on ignition was determined in all cases after the crushing and drying of the filter residue.

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• 1989
  • 1989-11-23 DE DE3938729A patent/DE3938729A1/de not_active Withdrawn
• 1990
  • 1990-11-14 BR BR909007867A patent/BR9007867A/pt not_active Application Discontinuation
  • 1990-11-14 JP JP3500630A patent/JPH05503066A/ja not_active Withdrawn
  • 1990-11-14 EP EP91900249A patent/EP0502083A1/de not_active Withdrawn
  • 1990-11-14 AU AU78957/91A patent/AU635846B2/en not_active Ceased
  • 1990-11-14 KR KR1019920701218A patent/KR920703447A/ko not_active Application Discontinuation
  • 1990-11-14 WO PCT/EP1990/001947 patent/WO1991008169A1/de not_active Application Discontinuation
  • 1990-11-14 CA CA002069477A patent/CA2069477A1/en not_active Abandoned
  • 1990-11-14 HU HU9201697A patent/HUT61247A/hu unknown
  • 1990-11-14 US US07/859,427 patent/US5215732A/en not_active Expired - Fee Related
  • 1990-11-19 YU YU220590A patent/YU220590A/sh unknown
  • 1990-11-20 CN CN90110349A patent/CN1052645A/zh active Pending
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  • 1990-11-22 IE IE422490A patent/IE904224A1/en unknown
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  • 1990-11-23 AR AR90318451A patent/AR242543A1/es active
• 1992
  • 1992-05-21 FI FI922320A patent/FI922320A0/fi not_active Application Discontinuation

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