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 present invention relates to a process for the hydrothermal production of potassium silicate solutions with a high SiO 2 : k 2 O molar ratio by reacting a crystalline silicon dioxide with aqueous potassium hydroxide solutions.
• potassium silicate solutions - generally referred to as potassium water glass - are used for technical purposes.
• Potash water glasses of this type predominantly have a solids content of approximately 28 to 55% by weight and a molar ratio of silicon dioxide to potassium oxide of 2.0 to 4.2: 1.
• the production of potash water glasses on an industrial scale is generally carried out by melting quartz sand and potash together in suitable furnaces at temperatures in the range from 1400 to 1500 ° C. The melt which solidifies on cooling, the solid glass, is then dissolved in water in a further process step using pressure and elevated temperatures and, depending on the quality requirement, the solution obtained, if appropriate, filtered.
• this high-temperature melting process is very expensive, both in terms of equipment and in terms of the amount of energy required, and also leads to not inconsiderable emissions, such as dust, nitrogen oxides and sulfur oxides.
• hydrothermal processes for the preparation of aqueous potassium silicate solutions are also known and are described in a number of patent applications.
• these processes are based on amorphous silicon dioxide, that is to say essentially on fly dusts and naturally occurring amorphous silicon dioxide modifications.
• the process products obtained here are of poor quality due to the usual impurities in the fly dusts and the natural amorphous silicon dioxide compounds which are used as input materials, and can therefore be used only to a limited extent for technical products.
• DE-AS 2826432 relates to a process for the preparation of water glass solutions by reacting fly dusts, which are obtained when silicon or ferrosilicon alloys are obtained, with aqueous alkali metal hydroxide solutions at elevated temperatures and then filtering the solutions contained, which is characterized in that Fly dust treated with a 6 to 15% by weight aqueous alkali metal hydroxide solution at temperatures of 12 ° C to 190 ° C and a pressure of 2.9 to 18.6 bar in an autoclave, the weight ratio of alkali metal hydroxide solution to solid fly dust 2 : 1 to 5: 1.
• the potash water glass obtained here has a SiO 2 : K 2 O molar ratio of 3.76: 1.
• the airborne dust used as raw materials have a silicon content of 89 to 98% by weight, which according to the exemplary embodiments is always 90% by weight; the rest consists of impurities.
• DE-CS 26 09 831 relates to a process for the preparation of silicon dioxide-containing, environmentally harmful waste dusts from silicon metal and silicon alloy production to form silicas or silicates, which is characterized in that the following process steps I to m are combined:
• the alkali silicate solutions obtained in this way generally have a SiO 2 : Me 2 O molar ratio in the range from 3.3 to 5.0: 1.
• DE-OS 26 19 604 relates to a process for the production of liquid water glass from amorphous silicon dioxide and alkali hydroxide, which is characterized in that silicon dioxide dust in the form of fly ash, which has been separated from the exhaust gases from ferroalloy industries and other industries working with silicon furnaces , Alkali hydroxide and water are mixed in a certain weight ratio and then brought to a temperature between 75 and 100 ° C with stirring, after which the liquid obtained is cooled.
• the silica dusts used as the starting material for this water glass production have in generally has a silicon dioxide content of 94 to 98% by weight; the plague consists of impurities.
• the potash water glass obtained has a molar ratio of SiO 2 / K 2 O of 3.58: 1.
• the prior art described below relates to processes for the hydrothermal production of potassium silicate solutions from crystalline silicon dioxide, that is to say sand, and potassium hydroxide solution, which according to the processes of the prior art, however, only have an SiO 2 : K 2 O molar ratio of up to 2, 75: 1 can be implemented.
• DE-OS 33 13 814 relates, inter alia, to a process for the preparation of a clear solution of a potassium silicate, the molar ratio of silicon dioxide: potassium oxide being 2.75: 1, by digestion of crystalline silicon dioxide with an average grain size of between 0.1 and 2 mm which is passed through an aqueous solution of potassium hydroxide through a bed of silicon dioxide which is formed in a vertical tubular reactor without mechanical movement and which is fed from top to bottom with silicon dioxide and the aqueous solution of potassium hydride.
• Belgian patent 649739 relates to a process and an apparatus for the production of clear sodium silicate bases by dissolving a material containing silicic acid at high temperature and under pressure in aqueous sodium hydroxide solution, which is characterized in that the product consists of the excess material containing silicic acid and / or of the insoluble contaminated substances is separated by means of filter elements that are close to the Peaktorbodens are attached, said filtration is advantageously carried out under the temperature and pressure conditions, which are very similar to the Peaktions claim. In this way, aqueous potassium silicate solutions are also to be obtained.
• the present invention is based on the object of providing a process for the hydrothermal production of potassium silicate solutions by reacting a crystalline silicon dioxide with aqueous potassium hydroxide solution, in which potassium silicate solutions with molar ratios of SiO 2 / K 2 O of more than 2.75: 1 are achieved.
• the object according to the invention is achieved by using a specially tempered quartz which is reacted with potassium hydroxide solutions under special reaction conditions.
• the present invention thus relates to a process for the hydrothermal production of potassium silicate solutions with a high SiO 2 : K 2 O molar ratio by reaction of a crystalline one Silicon dioxide with aqueous potassium hydroxide solution, which is characterized in
• mäh as a crystalline silica uses a quartz tempered at temperatures in the range from over 1100 ° C to the melting point, and
• this annealed quartz with aqueous potassium hydroxide solution in a concentration range of 10 to 40 wt .-% at temperatures of 150 to 300 ° C and the corresponding pressures of saturated water vapor in a pressure reactor.
• the process according to the invention is technically easier to handle due to its one-stage process control and is therefore more cost-effective than the technically complex, large amounts of energy which are high and pollute the prior art, that is to say the high-temperature melting process followed by a solution step.
• the process according to the invention has the distribution that the technically important potassium silicate solutions with a molar ratio of SiO 2 : K 2 O of more than 2.75: 1 are obtained through the use of the quartz specially annealed according to the invention, which using non-tempered quartz as SiO 2 component is not possible.
• quartz tempered in this way preferably a cristobalite formed in this way, in the context of a hydrothermal synthesis under the conditions specified above, allows direct, single-stage production of aqueous potassium silicate solutions, which is a molar ratio of SiO 2, even with short reaction times : K 2 O of more than 2.75: 1. Even with short reaction times, a high degree of conversion of the reaction components used can be achieved when using the process according to the invention.
• the use of a readily soluble crystalline silicon dioxide modification makes it possible to produce potassium silicate solutions with a high silicon dioxide / potassium oxide molar ratio, this taking place in high space / time yields with minimal energy consumption.
• the potassium silicate solution thus obtained preferably has an SiO. : K 2 O molar ratio of more than 2.75 to 4.2: 1, particularly preferably from 2.8 to 4.2: 1 and in particular from 3.1 to 4.0: 1.
• the aqueous potassium silicate solution is obtained by using a quartz tempered at temperatures of 1200 to 1700 ° C with the addition of catalytic amounts of alkali as crystalline silicon dioxide, which essentially converts to cristobalite under these tempering conditions, and in that the quartz thus tempered is reacted with aqueous potassium hydroxide solution in a concentration range from 15 to 30% by weight, preferably 15 to 25% by weight, at temperatures from 200 to 230 ° C. and the pressures of saturated water vapor corresponding to these temperatures in a closed pressure reactor.
• cristobalite is a crystal modification of silicon dioxide. This is practically exclusively produced synthetically by calcining quartz, by continuously converting quartz sand at temperatures of approx. 1500 oC with the addition of catalysts (alkali compounds). With regard to more detailed information on cristobalite, reference is made to Ullmarn's Encyclopedia of Industrial Chemistry, Volume 21, 4th Edition, 1982, pp. 439-442. For the purposes of the invention, it is therefore particularly preferred to use as the crystalline silicon dioxide a quartz tempered at temperatures in the range from 1300 ° C. to 1600 ° C. with the addition of catalytic amounts of alkali, which essentially converts to cristobalite under these conditions. It is also particularly advantageous to use a freshly tempered, yet warm cistobalite material for the process according to the invention.
• the reaction is carried out in the reactor by using an excess of tempered quartz of up to 100 mol%, preferably 2 to 30 mol%, based on the desired target SiO 2
• reaction can also be carried out with excesses greater than 100 mol% of tempered quartz; however, this is generally not technically sensible.
• peactors which are also customary for the hydrothermal synthesis of sodium silicate.
• These include e.g. rotating loosers, standing solver arrangements, peactors with agitators, jet loop reactors, tubular reactors and in principle all reactors which are suitable for the conversion of solids with liquids under pressure.
• Such reactors are described in detail, for example, in DE-OS 3002 857, DE-OS 3421158, DE-AS 28 26432, BE-PS 649739, DE-OS 3313814 and DE-PS 968034.
• potassium silicate solutions (potassium water glass solutions) prepared in the manner according to the invention can be used for all common uses which are known to the person skilled in the art and are described in the relevant literature, for example as adhesives, as binders in paints, foundry auxiliaries, Catalyst supports, welding electrode compounds, as a component in detergents and cleaning agents, and as a component for refractory materials.
• the invention is explained in more detail below by examples.
• the examples were made on a laboratory scale and on an industrial scale.
• a cristobalite obtained by annealing at 1300 to 1600 ° C and alkali catalysis was used as the annealed quartz in the exemplary embodiments.
• the pressure vessel rotated at a speed of 6 rpm around a horizontal axis.
• the heating was carried out with steam of 20 bar via an opening in the axis and an attached pipe with an effective distribution directly into the reaction container.
• the crystalline SiO 2 used for the examples contained> 99.0% by weight SiO 2 .
• the aqueous potassium hydroxide solution (potassium hydroxide solution) required for the process was heated with vapors from the pre-batch to about 103 ° C. using a venturi nozzle near the potassium hydroxide solution storage container.
• the quantities of substance (cristobalite / potassium hydroxide solution) were recorded using weighing devices.
• the raw materials were filled into the reactor, which was then sealed and set in rotation.
• the reaction mixture was heated to the reaction temperature of about 215 ° C. by direct introduction of steam and kept at this temperature. After a reaction time of 30 to 120 min at this temperature, the reactor was brought to a standstill and the reaction mixture was transferred via a flanged pipeline by means of its own pressure into a blow-out container.
• reaction mixture was then separated into vapors and water glass solution at about 105 ° C. using a cyclone separator.
• the vapors were aspirated by a jet apparatus and used to preheat the mixed liquor of the next batch in a venturi until the caustic boiling point limit of about 103 ° C.
• the potassium silicate solutions prepared were analyzed for their SiO 2 and K 2 O content.
• Example 1 The conditions of Example 1 were chosen as reaction conditions on an industrial scale.
• the batch size was 22,000 kg.
• the approximately 40% potassium water glass solution obtained had an SiO 2 : K 2 O molar ratio of 3.75: 1 and practically corresponded to the result of the experiment on a laboratory scale.
• the hydrothermal process using cristobalite / KOH solution can take place at relatively high solid concentrations in the reactor, since even at high SiO 2 : K 2 O molar ratio under reaction conditions (215 ° C / 20 bar) the potassium silicate solution has a viscosity range sufficient for the process.
• the potassium silicate solution that has reached the discharge container via the blow-out line is sufficiently diluted in such a way that the potassium silicate solution has a flowable, sufficiently low-viscosity consistency in the receiver at temperatures of approximately 100 ° C. before further processing by sedimentation or filtration having.
• This modification of the process has the particular advantage that if the solids concentration is high during the hydrothermal reaction in the reactor, the space / time yield (kg solids / m 3 reactor volume) is extraordinarily high, and the reaction product obtained is diluted outside the reactor on the way to the blow-out container.
• Example 1 demonstrates a batch which is favorable with regard to the relatively low starting liquor concentration when using stoichiometric cristobalite, based on a molar ratio of SiO 2 : K 2 O to be achieved in the potassium silicate solution of 3.96: 1.
• quartz was used.
• the addition of catalytic amounts of alkali at temperatures of 850 ° C. to 1600 ° C. is first annealed and then reacted hydrothermally with potassium hydride solution.
• untreated quartz was converted to potassium water glass in the same standard experiment of hydrothermal conversion with potassium hydroxide solution.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)
• Silicon Compounds (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1989
  • 1989-01-31 DE DE3902753A patent/DE3902753A1/de not_active Withdrawn
• 1990
  • 1990-01-12 KR KR1019900702102A patent/KR0125622B1/ko not_active IP Right Cessation
  • 1990-01-15 DD DD90337108A patent/DD291536A5/de not_active IP Right Cessation
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  • 1990-01-22 DE DE59008554T patent/DE59008554D1/de not_active Expired - Fee Related
  • 1990-01-22 WO PCT/EP1990/000116 patent/WO1990008733A1/de active IP Right Grant
  • 1990-01-22 EP EP90901791A patent/EP0456654A1/de active Pending
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  • 1990-01-22 BR BR909007068A patent/BR9007068A/pt not_active IP Right Cessation
  • 1990-01-22 AU AU48481/90A patent/AU623477B2/en not_active Ceased
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  • 1990-01-22 JP JP2502017A patent/JP2922290B2/ja not_active Expired - Fee Related
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  • 1990-01-29 CS CS90414A patent/CS276519B6/cs not_active IP Right Cessation
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• 1991
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• 1995
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