DE1767331A1 - Process for the production of alkali cyanide and silicon dioxide - Google Patents

Description

GERMAN GOLD AND SILVER SCHEIDEANSTALT FORMERLY ROESSLER Frankfurt / Main, Weisafrauenstr. 9

Process for the production of alkali cyanide and silicon dioxide .

The invention relates to a process for the preparation of alkali metal cyanide and silicon dioxide from alkali metal salts of weak Acids due to the action of acids.

It is known both alkali cyanides and silicon dioxide from alkali metal salts of weak acids through the action of acids produce, with alkali metal cyanides by reacting alkali metal carbonates with hydrocyanic acid and silicon dioxide by reacting alkali silicates with inorganic or organic acids can be obtained.

In addition to the. classic Castner and Bucher processes which alkali metal cyanides are produced from the elements, processes are also known, alkali metal cyanide, in particular Sodium cyanide, from alkali carbonates with hydrocyanic acid to the corresponding To implement cyanide. However, in order to avoid the stronger carbonic acid from the weaker hydrocyanic acid from soda or hydrogen- ' To release carbonate, higher temperatures of 360 to 900 C are required, which makes this process expensive and designed uneconomically.

For the production of silica gel or finely divided silicon dioxide, one generally starts from the raw materials water glass and mineral acid. While an unstable sol is initially obtained for the production of a gel by working with an excess of acid (mostly H-SO2 or HCl) and adding the water glass, the procedure is reversed to obtain finely divided SiOp. Here the water glass is usually presented and by adding acids (also flue gas C0 ₂ )

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SAD ORIGlNAU

the flocculation achieved. According to another known method, the acid and water glass are allowed to run separately into a solution provided, which is kept neutral during the reaction becomes (7 - 7 »5 pH). In an alkaline medium, down to pH 7, easily dispersible substances arise, while in the Acid gel precipitation firmly adhering particles are formed, which are combined to form hard spheres. Since the Silica in the alkali silicate as a very weak acid can be released by any stronger acid, the implementation can be carried out at room temperature or, for faster reaction, at elevated temperatures of up to 8o C.

These and other known processes for the production of SiO "

however, all have the disadvantage that the total alkali content

of the water glass with consumption of e.g. sulfuric acid is lost as sodium sulfate.

The invention was based on the object, a method for the production of alkali cyanide and silicon dioxide from alkali metal salts of weak acids by the action of acids indicate by means of which the disadvantages in cyanide and silicon dioxide production are avoided.

The characteristic of the invention can be seen in the fact that the alkali salt of a weak acid is an alkali silicate and as Acid hydrogen cyanide can be used.

It has been found, surprisingly, that by using alkali water glass and hydrogen cyanide in one Composite process at the same time alkali cyanide and silicon dioxide can be obtained in good yield, with neither high Temperatures need to be applied, there are still by-products which are lost or their by washing Recovery is too expensive.

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BATH ORIGINAL

Implementation in the joint process can be carried out according to the Process sequences described below with the aid of schematic representations are carried out.

Implementation of alkali water glass solutions with hydrocyanic acid in the aqueous phase (Scheme 1.) s

The precipitation process and, depending on it, the filterability and Grain size (surface m / g SiO) of the precipitated silica can be controlled, among other things, by using commercially available Alkali water glass solutions diluted with water accordingly (l).

This water addition is taken from the first washing stage (v). Alkali cyanide, which still adheres to the precipitated silica (IV), is washed out by fresh water and used to dilute the water glass solution.

The precipitation (Hl) can be by gaseous or liquid or aqueous hydrocyanic acid solutions are carried out. The filtrate of the precipitated silica (iv) is freed from the unreacted, dissolved silicate by adding CH 2 OH (XIII). After the separation (XIV) this silicate is returned in stage I or III, while the filtrate is determined to be NaCN solutions Concentration or is concentrated to solid NaCN. The CIUOH required for precipitation (XIII) is obtained by rectification (XVl) recovered and used again in stage XIII.

The precipitated silica passes through III after separation a security wash (VII -IX). This aftercare with Dilute acid (e.g. HCl) (possibly waste acid) not only has the task of reintroducing any NaCN that may still be present To transfer hydrogen cyanide, but also to remove unreacted alkali. The temperature should be above this if possible

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BATH ORIGINAL

the boiling point of the HCN. The diluted acid is circulated and in the stripping column of possibly Existing hydrocyanic acid residues are freed. The combined hydrogen cyanide residual gases are fed back into the precipitation process.

At this point (VII - IX) a CO take place.

Implementation of solid alkali waterglass with hydrocyanic acid in organic or aqueous-organic solvents (alcohol · see phase (scheme 2) ι

The solvent or solvent mixture used must meet the following conditions:

Alkali water glass or SiO ₀ must not be soluble in this, the NaCN formed, on the other hand, must be soluble «Methanol or aqueous-methanolic solutions have proven to be the most suitable.

The grain size (surface) of the desired silica is determined by the grinding or classifying process for the water glass starting product used (i + II).

The reaction takes place by introducing hydrocyanic acid into a slurry of the alkali water glass in the above

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Solvent or solvent mixture in the reactor (ill). After the separation of the solid SiO _{2 formed} from the. NaCN solution in (aqueous) methanol (iv), the piltrate is evaporated to dryness (VIl). The recovered solvent or solvent mixture is fed to stage (ill), a partial stream of this to the washing process (ν), in which NaCN residues are extracted by means of (aqueous) methanol. After the separation (VI) of the cleaned-off SiO from the NaCN / solution mixture, the piltrate goes back to the evaporation (VIl). The remaining solvent, which is retained by the silica after separation (VI), is driven off in an evaporator (not shown). The silica obtained is subjected to an aftertreatment (see scheme X, VII-XIl) to remove unreacted alkali.

Production of and reaction with finely divided, solid alkali waterglass (Scheme 3) '-

Alkali water glass can be made from commercially available alkali water glass solutions, which can be additionally diluted with water as required by adding organic solvents, which are miscible with water, are precipitated in the finest form « Alkylamines (trimethylamine, Triethylamine, diethylamine). Acetone and alcohols can also be used. However, alcohols dissolve from the alkali water glass Alkali out.

Trimethylamine proved to be the most suitable. The trimethylamine can be easily recovered due to its low boiling point. The precipitated alkali water glass, but also the silicic acid obtained by acid aftertreatment, can be filtered very easily and the SiO _{2 obtained} is characterized by a high DBA number (y 3oo),

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BATH ORIGINAL

After precipitation and filtration (II + III) the filtrate is over a column (VI) is distilled and the recovered organic solvent is used again in the precipitation process (il). The organic adhering to the precipitated alkali water glass Solvent residues are expelled into (V) after the separation (ZV).

The further processing of the solid, finely divided material obtained in this way Alkali water glass is then carried out according to scheme 2 in the alcoholic phase with hydrocyanic acid or with another acid, which is preferably inert towards the alcoholic phase under the conditions of the reaction, e.g. carbonic acid.

Advantageous embodiments are illustrated in the following examples of the process sequences according to schemes 1 to 3 are reproduced, but without the invention being dependent on this should be limited.

In all examples it should be noted that the Alkali water glass should be as low in carbonate as possible. The metering the hydrocyanic acid takes place in accordance with the proportion of alkali silicic acid. Due to possible polymerization phenomena an excess of hydrocyanic acid is to be avoided. In the best case scenario, hydrogen cyanide could be added equivalent to the total alkali of the alkali waterglass solution.

Examples I and II correspond to schemes 1 and 2, the other examples III to XI correspond to scheme 3

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BATH ORIGINAL Examples:

I. In a 2 liter three-necked flask, 417 g sodium waterglass solution (27 ^ SlOgJ 7.9 # Na ₂ O) with a content of 31.6 g = 0.779 mol NaOH are placed and diluted with 417 g water. With vigorous stirring and reflux, 2k gs of 0893 mol of liquid hydrocyanic acid are then added dropwise at room temperature. The silica precipitates in finely divided form after the first drop of hydrocyanic acid. 6Uo g of water are added after about 2/3 the amount of hydrocyanic acid, so that a stirrable suspension remains. After a reaction time of about 1 hour, the precipitated silica is knocked off using a water jet vacuum. The filtrate is processed into NaCN solutions of a certain concentration or into solid NaCN.

The residue is slurried again in 1000 g of water and filtered again. Then 20 g of the The residue treated with hot, approx. 15% hydrochloric acid, washed and dried.

In the silica obtained in this way, neither by titration according to Liebig nor by the Berlin blue reaction (Na digestion) cyanide can be detected.

After the excess hydrocyanic acid has been driven off, 1.1052 g of the 1st filtrate consume 6.45 ml of 0.05 η Ag N0 “solution. The total amount of the 1, filtrate (150 g) thus contains 33 g of NaCN = 85 1 * of theory.

II. In a 25o ml three-necked flask 58,5 S according to the procedure generally according to Scheme 3 obtained finely divided dry sodium silicate with 9.5 $ Na ₃ O as NaOH at room temperature in 97 g of an aqueous methanol solution (92 g of CII ^ OH; 5 g water) slurried. Under

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6AD ORIGINAL.

. 8 g = 0.296 mol of liquid hydrocyanic acid are then added with vigorous stirring and reflux. After a reaction time of about 1 hour, the solid is filtered off with suction using a water jet vacuum. The filtrate is processed into NaCN solutions of a certain concentration or into solid NaCN. The residue is slurried again in 97 g of aqueous-methanolic solution (92 g of CH.OH; · 5 g of H ₂ O) and suction filtered. 20 g of the residue were treated with hot, approx. 15% hydrochloric acid, washed and dried. After that, cyanide could not be detected in the silica either by titration according to Liebig or by the Berlin blue reaction (Na digestion).

After the excess hydrogen cyanide had been driven off, 41.2 ml were obtained in the Liebig filtration for 5,626 g of the 1st filtrate o, o5 η Ag N0_ solution consumed.

97 g of the mother liquor thus contain 3. ^ 8 g NaCN «39.5 % of theory.

III. To 7oo g = 11.85 mol of trimethylamine, 357 g of sodium silicate solution (27 $ SiO_; 7.9% Na ₂ O) are added with stirring over the course of four minutes. (Molar ratio of water to trimethylamine »12.9 '· 11.85 = 1 i 1, o9). The soda water glass precipitates out in a scale-like manner and quantitatively. (Filtration residue (moist): 256 g).

After adding liquid HCN or 15 # hydrochloric acid wins an easily filterable silica. After washing and drying, it has a DBA number of 323 meq / kg.

IV »To a mixture of 72o» 12.2 mol of trimethylamine and 50 g of β 1.56 mol of methanol, 357 g of ^{sodium waterglass solution} _{(27 # SiO 2} » 7.9 # Na ₃ O) are added with stirring over the course of four minutes. (Molar ratio water / solvent mixture «12.9 t 13.76 e-1: o.93) (filtration residue (moist): 266 g). The properties of the product obtained correspond to those of Example III.

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BATH ORIGINAL

The DBA number of the with liquid HCN or 15 # hydrochloric acid treated, washed and dried product is 321 meq / kg.

V. To a mixture of 72o g = 12.2 mol of trimethylamine and 1oo g = 3.12 moles of methanol are added under stirring within 4 minutes, 357 g of sodium silicate solution (27 i "SiO _2; 7.9% Na ₂ O) was added. (Molar ratio water: solvent mixture = 12.9: 15.32 β 1: ο, 84) (Filtration residue (moist) ι 3o5 g) The properties of the product obtained correspond to those of Example III,

The DBA number of the washed and dried product treated with liquid HCN or 15 # hydrochloric acid is 326 meq / kg.

VI. 357 S sodium waterglass solution (27 $ SiO ₂ ; 7.9 $> Na ₂ O) are added to 750 g ss 7.42 mol of triethylamine with stirring over the course of 15 minutes. (Molar ratio of water, triethylamine ss 12.9 ι 7.42 = 1.73: 1), the sodium silicate precipitates practically quantitatively. The flaky precipitate can be filtered very easily (filtration residue (moist): 242 g).

After adding liquid HCN or 15% hydrochloric acid an easily filterable silica is obtained »After washing and drying it has a DBA number of 7o.4 meq / kg.

VII, To a mixture of 750 g = 7.42 mol of triethylamine and 25 g = 0.78 mol of methanol, 357 g of sodium waterglass solution (27 # SiO ₂ ; 7.9 ia Na ₂ O) are added with stirring over the course of 15 minutes. (Molar ratio of water to solvent table = 12.9 ι 8.2 »1.57 1) (Filtration residue

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BATH ORIGINAL

(moist): 275 g) · The properties of the extracted Product correspond to those of Example VI.

The DI3A number of the with liquid HCN or 15 # hydrochloric acid treated, washed and dried product is 78.4 meq / kg.

VIII. To 3oo g = 4.11 mol of diethylamine are added 150 g of sodium waterglass solution (27 $ SiO ₂ ; 7.9 # Na ₂ O) with stirring over the course of 15 minutes. (Molar ratio of water: diethylamine = 5.42: 4.11 = 1.32 j 1). The soda water glass precipitates practically quantitatively and is very easy to filter.

The DBA number of the with liquid HCN or 15 # hydrochloric acid treated, washed and dried product is 32 meq / kg.

IX. To a mixture of 300 g = 4.11 mol of diethylamine and 3o g = 0.94 mol of methanol, 150 g of sodium waterglass solution (27 $ SiO ₂ ; 7.9% Na 2 O) are added with stirring over the course of 15 minutes. (Molar ratio of water to solvent mixture ss 5 »42: 5» o5 = 1 | O7 '· 1) · The soda waterglass precipitates practically quantitatively and is very easy to filter.

The DBA number of the liquid HCN or 15 # salt r acid-treated, washed and dried product is 50 meq / kg.

X. To 400 g = 12.5 mol of methanol, 250 g of sodium waterglass solution (27% SiO ₂ ; 7.9 _{% Na 2} O) are added over the course of 15 minutes with stirring. (Molar ratio of water: methanol = 9 _f o4: 12.5 - o.72 s 1). The soda water glass falls out in the shape of a pearl.

The DBA number of the with liquid HCN or 15 # hydrochloric acid treated, washed and dried product is 8 meq / kg.

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BAD ORfGiNAL

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XI. _{250 g of sodium waterglass solution (27 $ SiO 2} ; 7.9% Na 2 O) diluted with 500 g of water are added to 400 g of 12.5 mol of methanol with stirring over the course of 30 minutes (molar ratio of water: methanol = 36.54: 12 , 5 »2.92 % 1). The soda water glass falls out in the shape of a pearl.

The DBA number of the liquid HCN or 15% hydrochloric acid treated, washed and dried product is 82 meq / kg.

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Claims (6)

Claims 1 ·) Process for the production of alkali metal cyanide and silicon dioxide from alkali metal salts of weak acids by the action of acids, characterized in that an alkali metal silicate is used as the alkali metal salt of a weak acid and hydrogen cyanide is used as the acid. 2.) The method according to claim 1, characterized in that an aqueous alkali silicate solution is reacted with gaseous or liquid hydrogen cyanide or its aqueous solution. 3.) The method according to claim 1, characterized in that a water glass dispersion whose liquid phase consists of an organic solvent or solvent mixture, in which alkali water glass and the silicon dioxide formed are insoluble, the alkali metal cyanide formed, however, is soluble, with gaseous or liquid hydrogen cyanide or whose aqueous solution is implemented. k.) Process according to Claims 1 to 3, characterized in that the reaction is carried out with a methanolic or aqueous-methanolic alkali metal silicate dispersion. 5 «) Process according to claims 1 to 4, characterized in that the reaction with a methanolic or aqueous-methanolic alkali metal silicate dispersion, which is obtained by precipitation of finely divided, solid alkali metal silicate from an aqueous alkali metal silicate solution with a water-miscible organic solvent, in particular with alkylamines or Acetone, separating the finely divided solid alkali silicate from the precipitant and dispersing in alcohol or a water-alcohol mixture is carried out. 109838/133 1 - 2 - 6.) Ancestors according to claims 1 to 5 » characterized in that sodium 11icate is reacted with hydrogen cyanide to form sodium cyanide and silicon dioxide. 109838/133 Empty soap