CS259587B1 - Process for preparing pure acetic acid - Google Patents

Abstract

The invention provides for the preparation of particularly pure acetic acid using physicochemical purification methods in a device made of materials that are resistant to the corrosive effects of acetic acid and its accompanying impurities. Acetic acid is discontinuously or continuously distilled under reduced or atmospheric pressure without air access. A fraction is taken at a defined intermediate temperature.

Description

The invention relates to the preparation of particularly pure acetic acid using physicochemical purification methods in a device made of a material that is resistant to the corrosive effects of acetic acid and its accompanying impurities. .·

Acetic acid is used as an etchant in the production of integrated circuits. For this purpose, acetic acid must meet strict purity criteria. The impurities found in this chemical, of ordinary commercial purity, can be classified into two groups.

The first group includes organic impurities that have entered the system as residues of unreacted input raw materials, impurities from these raw materials, and also products of side reactions.

The second group includes impurities of inorganic nature, such as metal ions from corrosion of production equipment, dust particles originating from contamination of chemicals with the surrounding air.

The above-mentioned shortcomings are not inherent in the method of preparing particularly pure acetic acid, the essence of which lies in the fact that acetic acid of a purity available according to ČSN 686 310 (i.e. purity pa or pure) is continuously or discontinuously distilled under reduced or atmospheric pressure in an apparatus whose material resists the corrosive effects of acetic acid. A fraction is taken at a temperature of t ₀ + 1 °C given by the dependence to

1572.32

6.5729 — log p

226.37 where t ₀ is the boiling point in °C corresponding to the working pressure at which distillation is carried out and p is the working pressure in the apparatus in kPa. The distillate is fed to a set of microfilters with a porosity of 0.8 μm to 0.2 μm.

The method for preparing particularly pure acetic acid is given in the example.

Example

Pure acetic acid from glass flasks of 50 to 100 l is pumped by a glass pump (SIMAX glass) into a glass reservoir (SIMAX glass). From there it is dosed into a glass evaporator (SIMAX glass). It is distilled continuously or discontinuously, at reduced or atmospheric pressure. All seals on the distillation equipment are made of Teflon. The distillate is collected in a glass receiver (SIMAX glass). If the content of dust particles in the distillate determined by the analyzer or in the laboratory is below the permissible limits, then the distillate is discharged by gravity or by a pump into glass shipping containers that have been previously freed from dust particles. The following quality indicators are prescribed for dust particles:

lie 5 μΐη 20,000 dm~ ³ to 25 μτα 3,000 dm ^-3 above 25 μΐη 500 dm ³

If the dust content is higher than the specified values, the distillate is pumped for filtration. The filtration device consists of a set of stainless steel filter holders, which serve to tension the filter material. The microfilter material must withstand the dissolving effects of acetic acid. The porosity of the microfilters is 0.8 μm, 0.45 μm and 0.2 μm. The distillate filtered in this way is filled into glass shipping containers.

Acetic acid of quality p. a. is analyzed according to ČSN 68 6310, which is supplemented by the determination of alkaline earth metals by atomic absorption spectrometry. The most important quality parameters for microelectronics are listed and, as a second piece of information, the measured values of the raw material used.

p. m. Mr. Main content j 99.8% 99.0% components vapor 5.0 ppm 20.0 ppm If 0.02 ppm — On 0.5 ppm — To 0.1 ppm — About 0.5 ppm 0.7 ppm Mg 0.1 ppm — Fe 0.1 ppm 1.0 ppm

Cu 0.02 ppm

Ni 0.02 ppm

Dust particle content:

1 to 5 μτα 20,000 ^dm3 163,000 5 to 25 μm 3,000 ^dm3 51,626 over 25 μη 500 dm ^-3 10,795

1000 liters of raw material are pumped into the distillation column reboiler (SIMAX glass) and distilled at a pressure of 17 kPa. A fraction is taken at a temperature of 66 °C. The distillation process yield was 80 Ψο with respect to the feed of raw material. The distillate is filtered on microfilters with a porosity of 0.8 μΐη to 0.2 μπι.

The obtained distillate is analyzed. The product has the following quality parameters:

Main ingredient content 99.6% vapor 5.0 ppm If 0.05 ppm On 0.05 ppm To 0.05 ppm Mg 0.01 ppm About 0.05 ppm Fe 0.03 ppm Cu 0.01 ppm Dust particle content: 1 to 5 μτα (582 dm ^-3 5 to 25 μΐη 495 dm ^-3 over 25 mτα 344 dm ^-3

Claims (1)

SUBJECT We claim: A method of synthesis of pure acetic acid from the pre-formed acetate characterized in that the acetic acid is distilled at reduced or atmospheric pressure in the apparatus, wherein the material is resistant to the corrosive effects of distilled medium, absence of air, obtaining fractions at a mean temperature T _{of the} + 1 ° C, given by dependence where t ₀ is the boiling point in ° C corresponding to the working pressure at which it distills and p is the working pressure in the apparatus in kPa, and the distillate is fed directly through a microfilter set having a porosity of 0,8 μΐη to 0 , 2 μτη.