Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/26—Separation of sediment aided by centrifugal force or centripetal force
  • B01D21/262—Separation of sediment aided by centrifugal force or centripetal force by using a centrifuge
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1456—Removing acid components
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1493—Selection of liquid materials for use as absorbents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/96—Regeneration, reactivation or recycling of reactants
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/0018—Evaporation of components of the mixture to be separated
  • B01D9/0031—Evaporation of components of the mixture to be separated by heating
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C3/00—Cyanogen; Compounds thereof
  • C01C3/02—Preparation, separation or purification of hydrogen cyanide
  • C01C3/0208—Preparation in gaseous phase
  • C01C3/0212—Preparation in gaseous phase from hydrocarbons and ammonia in the presence of oxygen, e.g. the Andrussow-process
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C3/00—Cyanogen; Compounds thereof
  • C01C3/08—Simple or complex cyanides of metals
  • C01C3/10—Simple alkali metal cyanides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
  • C01D13/00—Compounds of sodium or potassium not provided for elsewhere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/60—Inorganic bases or salts
  • B01D2251/604—Hydroxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/408—Cyanides, e.g. hydrogen cyanide (HCH)
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency
  • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Definitions

• the present invention relates to a method for producing alkali metal cyanides as solids and alkali metal cyanides produced according to this method.
• Alkali metal cyanides have numerous applications. One particularly important area of application is the use for obtaining gold, silver, and other metals in cyanide leaching. Other areas of application are electroplating technology and also hardening steel. Alkali metal cyanides find numerous applications as a starting material in chemical synthesis. One example here is the use for the synthesis of nitriles, which have manifold applications in the chemical industry. One alkali metal cyanide which is particularly industrially important is sodium cyanide.
• HCN hydrogen cyanide
• alkali metal hydroxides An array of methods has been described in the prior art for the industrial production of HCN as a starting substance for this synthesis of alkali metal cyanides.
• One particularly frequently used method is the so-called Andrussow method.
• the Andrussow method the production of HCN is performed by catalyzed reaction of methane, ammonia, and air oxygen.
• methane, ammonia, and air oxygen In this case, a mixture of ammonia and methane is typically brought to reaction at high temperatures on platinum nets with injection of oxygen.
• the synthesis product produced directly by the Andrussow method represents a mixture of multiple components in this case, wherein in particular unreacted ammonia, hydrogen, nitrogen, and carbon oxides are present in addition to the desired reaction product HCN.
• the HCN-containing reaction gas is liquefied by cooling after the reaction and subsequently the hydrocyanic acid is purified.
• Complex purification methods for example, rectification, are necessary for this purpose.
• the liquid hydrocyanic acid thus purified is then, according to this method from the prior art, brought to reaction with alkali metal hydroxide, typically sodium hydroxide, to obtain sodium cyanide. If the sodium cyanide is to be produced as a solid, crystallization thus has to be performed in a further step.
• the sodium cyanide mother liquor can be recirculated after the recrystallization into the reaction container in which the liquefied hydrocyanic acid is brought to reaction with sodium hydroxide.
• this procedure does not result in a closed loop, since byproducts, for example, sodium formate, become enriched in the course of multiple recirculation cycles, so that after a certain time, the sodium cyanide mother liquor can no longer be recirculated.
• the sodium cyanide mother liquor thus contaminated by byproducts then has to be disposed of in a costly and environmentally-harmful manner.
• This disposal is particularly complex because sodium cyanide and other alkali metal cyanides are highly toxic.
• the disposal is performed by adding hydrogen peroxide, wherein the sodium cyanide is oxidized to form sodium cyanate. In some circumstances, still further steps are necessary before a final disposal of the detoxified wastewater can be performed. This results in a high cost expenditure.
• the present invention is based on the object of providing a method for producing alkali metal cyanides as solids, which avoids the above-described disadvantages.
• the present invention is based on the object of providing a method for producing alkali metal cyanides, which enables the production of alkali metal cyanides as solids in the fewest possible method steps, and at the same time creates as little waste as possible, which has to be disposed of in a complex manner.
• the object according to the invention is achieved by a method for producing alkali metal cyanides as solids, which comprises the following steps:
• a crystallization step in the form of the introduction of the alkali metal cyanide solution into an evaporative crystallizer, which is heated by steam heating so that at the contact surface of the heating element with alkali metal cyanide solution, a temperature of approximately 60-100° C., preferably approximately 70-90° C. is provided, and in which a pressure of approximately 30-100 mbar (a), preferably 60-65 mbar is provided;
• step iv) a recirculation step in the form of the recirculation of X vol. % of the mother liquor separated in step iii) into the absorption and the recirculation of (100-X) vol. % of the mother liquor separated in step iii) into the crystallization according to step ii);
• step v) a drying step in the form of the drying of the alkali metal cyanide crystals separated in step iii), wherein the drying step is designed in particular so that the separated alkali metal cyanide crystals are dried by means of a contact dryer connected downstream and the degree of drying of the alkali metal cyanide crystals can be set individually from batch to batch.
• An entirely essential step of the method according to the invention is the partial recirculation of the alkali cyanide mother liquor into the absorption process, i.e., the step of the reaction of the synthesis gas containing hydrogen cyanide with the alkali metal hydroxide solution.
• the remaining component of the mother liquor separated in separation step iii) is recirculated in this case into the crystallization according to step ii).
• the setting according to the invention of the parameters in the crystallization step ii) is of particular significance in this case.
• the heating of the crystallization solution in step ii) is typically performed in this case by a pipe bundle heat exchanger which is heated using steam on the jacket side.
• vacuum steam is preferably used, so that temperatures of approximately 70-100° C., typically approximately 70-90° C. are achieved.
• the formation of byproducts, in particular in the form of formates, can be substantially suppressed by these low temperatures.
• crystal sizes are achieved by the interaction of these method parameters with respect to the heating with the vacuum generation in which a pressure of approximately 30-100 mbar, preferably approximately 60-65 mbar is provided. Crystal sizes of approximately 100-120 ⁇ m are desired. Nearly complete separation of the crystallized-out alkali metal cyanides from the crystallization solution is thus possible.
• the formation of byproducts in particular in the form of formates, can be suppressed so substantially that in cooperation with the procedure according to the invention of the partial recirculation of the mother liquor separated in step iii) into the absorption (step i)) and recirculation of the remaining part of the mother liquor into the crystallization (step ii)) it is thus possible for the first time to produce a closed loop of the alkali metal cyanide solution.
• the method according to the invention therefore enables the production of alkali metal cyanide as a solid in good quality with only minor contaminants, wherein at the same time no wastewater containing alkali metal cyanide results, which has to be disposed of in a costly and environmentally-harmful manner.
• an alkali metal cyanide in the form of sodium cyanide is produced by the method according to the invention.
• sodium hydroxide sodium hydroxide solution
• step i the alkali metal hydroxide solution.
• a further advantage of the method according to the invention is that in step i), the synthesis gas containing hydrogen cyanide can be used as a non-purified gas mixture directly from an Andrussow process. It is possible by way of the method control according to the invention to bring the HCN-containing gas mixture formed in an Andrussow process directly into reaction with the alkali metal hydroxide solution without any interposed purification step.
• the alkali metal cyanide crystals formed in step iii) have a grain size distribution having grain sizes d50 of approximately 50-200 ⁇ m, in particular approximately 100-120 ⁇ m.
• step iii) It has also proven to be particularly advantageous for the separation of the formed alkali metal cyanide crystals in step iii) to be performed at a solid concentration of approximately 5-40 mass-%, in particular approximately 10-30 mass-%.
• the recirculation is performed so that the percentage component X vol. % of the mother liquor separated in step iii), which is recirculated into the absorption (step i)), is approximately 5-40 vol. %, in particular approximately 10-20 vol. %. Accordingly, the component (1 ⁇ X) vol. % of the mother liquor separated in step iii), which is recirculated into the crystallization (step ii)), is advantageously approximately 60-95 vol. %, in particular approximately 80-90 vol. %.
• the method according to the invention is designed so that the steps i), ii), iii), and iv) represent a closed loop with respect to the mother liquor separated in step iii), in the case of which no mother liquor containing alkali metal cyanide has to be discarded over numerous method cycles.
• the alkali metal hydroxide is preferably continuously measured and regulated, so that the optimum concentration of the alkali metal hydroxide is always provided. It is possible by way of this continuous measurement and regulation to always keep the content of free alkali metal hydroxide in the solution in the desired range of approximately 2-10 wt. %.
• the drying step v) of the drying of the alkali metal cyanide crystals separated in step iii) is performed so that the drying occurs in a contact dryer with forced circulation at a temperature of the heating medium of approximately 180-400° C., preferably approximately 185-250° C.
• dryer and preheater The interaction of dryer and preheater is preferably designed in this case so that dryer and preheater are flushed with a preheated airflow such that targeted air guiding from the outside to the inside and from dry to damp occurs.
• a further special advantage of the method according to the invention is that in step i), a synthesis gas containing hydrogen cyanide can be used, for the production of which natural gas having a methane content of approximately 98 mass-% can be used without special prior purification for the Andrussow process.
• the reaction product of the Andrussow process which was produced from a natural gas thus used having a methane content of approximately 98 mass-% can be used directly for absorption in step i) without intermediate purification steps.
• the step v) is followed by a further step vi) in the form of a pulverization step, wherein a setting of the maximum size of approximately 10 mm for optimizing the subsequent briquetting is performed for pulverizing contacts of the alkali metal cyanide crystal flow from step v).
• the present invention also relates to an alkali metal cyanide, in particular in the form of sodium cyanide, which is produced according to the method according to the invention.
• the method according to the invention has numerous advantages in relation to the previous methods for producing alkali metal cyanides.

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• 2015
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