RU2232745C1 - Method for preparing acetic acid aqueous solution - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for preparing acetic acid an aqueous solution. The following steps are carried out for the method realization. Supple tank is filled with calculated amount of water and acetic acid for preparing acid solution in the concentration 20-55 wt.-% in the amount 15-30% of the supply tank volume. Then solution is stirred by circulation, volume of prepared solution, temperature, density and mass part of acetic acid are determined. Then the second filling the supply tank is carried out with the parent 72-80% acetic acid solution up to the required volume, the content of supply tank is stirred with simultaneous bubbling the solution using air inflow into indicated capacity for 5-30 min. The solution is homogenous at equal values of temperature, density and mass part of acetic acid in upper and lower layers. The procedure for stirring solution by bubbling is repeated in the case of absence of homogeneity of solution. Then correction of solution is carried out by addition of water or acid to the required mass part of acetic acid in solution that is 70 ± 1%. Invention provides reducing inflammability in technological process and reducing the concentration of acetic acid vapors in working compartment.

EFFECT: improved preparing method.

1 dwg, 5 ex

Description

The invention relates to the field of organic chemistry, in particular to the preparation of an aqueous solution of acetic acid.

A known method of producing 70% acetic acid (Technological instruction for obtaining 70% acetic acid TI 10-02000334586-02, developed by the All-Russian Research Institute of Food Biotechnology, Moscow, 2002), which consists in the fact that an 80% solution is loaded into the reactor acetic acid, pour the calculated amount of water, mix, take a sample to determine the mass fraction of acetic acid, if the specified concentration does not match, it is adjusted to the desired one by adding water or acetic acid.

The disadvantage of this method is the fire hazard and toxicity of the process due to the high partial pressure of acetic acid in saturated vapors. This requires the careful sealing of equipment and the installation of a vapor recovery system.

The closest in technical essence is the method of producing 70% acetic acid (Technological regulations of SibPromChem LLC for the production and packaging of acetic acid, approved March 30, 1999). It consists in the fact that the pressure vessel is filled with the initial solution of acetic acid with a mass fraction of the main substance of 72-80%, mixed in this vessel by circulation, the volume of the obtained solution, the density, temperature and mass fraction of acetic acid are determined, then the calculated amount of water is introduced. mix the resulting solution by circulation, determine the mass fraction of acetic acid. If the main parameter deviates from the preset 70 ± 1%, an adjustment is made by supplying water or acetic acid with the initial concentration.

The disadvantages of the prototype are the following:

- a high concentration of acetic acid vapor in the air of the working area, exceeding the MPC (5 mg / m ³ );

- the fire hazard of the feedstock into the working tank, since 80% acetic acid is a flammable liquid, and 72-80% acid is a combustible liquid;

- loss of raw materials as a result of evaporation;

- the need to seal equipment and establish a complex vapor recovery system.

The aim of the invention is to reduce the fire hazard of the process and reduce the concentration of acetic acid vapor in the air of the working area.

This goal is achieved in that in a method for producing an aqueous solution of acetic acid, comprising first filling a pressure vessel with an aqueous solution of acetic acid, stirring the solution by circulation, determining its volume, temperature, density and mass fraction of acetic acid, second filling the pressure vessel with the missing ingredients to obtain the required amount of 70 ± 1% acetic acid, the second mixing of the resulting solution, determining the volume, temperature, density and mass fraction of acetic acid , in the event of a deviation from a predetermined solution concentration of 70 ± 1%, an adjustment is made by loading water or acetic acid. According to the invention, the first filling of the pressure vessel is carried out by introducing the calculated amount of water and acetic acid to obtain a solution with a mass fraction of acetic acid of 20-55% in the amount of 15-30% of the volume of the pressure vessel, the second filling of the pressure vessel is carried out by the initial 72-80% solution acetic acid to a predetermined volume, the second mixing of the contents of the pressure vessel is carried out with the simultaneous bubbling of a heterogeneous solution by suction of air into the specified container for 5-30 minutes In order to assess the homogeneity of the solution, the density, temperature and mass fraction of the main substance in the upper and lower layers are determined. Next, the mass fraction of acetic acid is adjusted. In case of inhomogeneity of the solution, the operation of mixing with bubbling is repeated.

This method allows you to create a water cushion with a mass fraction of acetic acid of 20-55% during the entire stage of loading fire-hazardous raw materials. In this range, acetic acid is in monomeric form, which leads to the absence of fire hazard and low partial pressure of acetic acid in saturated vapors.

The drawing shows a diagram of a device for implementing the method.

The technological process is as follows.

In the pressure tank 2, which is a rectangular parallelepiped with a capacity of 5000 dm ^3, through the suction pipe 4 with the open valve 7 using the pump 5 (capacity 6 m ³ / h), the calculated amount of water and the initial 72-80% acid are fed through the supply pipe 6 in the amount of 15-30% of the volume of the pressure vessel 2 and mix the solution by circulation with closed valves 7, 10 and open 8, 9. Next, determine the volume of the resulting solution using a level gauge, through the valve 11 take a sample and determine the density, temperature and mass the proportion of acetic acid. Similarly to the above, a second filling of the pressure vessel 2 with the initial 72-80% solution to the specified volume is performed. Then, a second mixing of the contents of the pressure vessel 2 is carried out with the valve 9 open and the half-open valves 7, 8 so as to ensure the simultaneous bubbling of the heterogeneous solution by suction of air through the suction pipe 4 for 5-30 minutes. After that, in order to assess the homogeneity of the solution, the upper and lower layers are analyzed by density, temperature and mass fraction of the main substance. In the absence of homogeneity, the mixing operation with bubbling is repeated. In the case of homogeneity of the solution, the operation of adjusting the main parameter is carried out similarly to the prototype.

70 ± 1% acetic acid from the point of view of the consumer is the most safe in terms of toxicity and fire hazard (GOST 6968-76 “Acetic acid, wood-chemical”).

The invention is illustrated by the specific examples given in the table.

Example 1

At the first filling, 2,275 kg of water is fed into the pressure vessel; 700.4 kg of acid with a mass fraction of the main substance (C) of 69.1%, stirred by circulation for 3 minutes and get 975.4 kg of a solution of acetic acid with T = 14.35 ° C, density ρ = 1.0615 g / cm ³ and mass fraction of the main substance C = 49.6%, which is a water cushion for the feedstock. At the second filling, 4013.2 kg of acetic acid with a mass fraction (C) of 80.4% is fed into the pressure vessel. Analyze the upper layer: its T = 14.00 ° C, density ρ = 1.0620 g / cm ³ and the mass fraction of the main substance (C) 49.8%. We see that the water cushion is preserved. Mixing is carried out by circulation with bubbling for 10 minutes. Again analyze the upper and lower layers. Receive respectively for the upper layer T = 13.4 ° C, ρ = 1.0755 g / cm ³ , C = 72.6%, for the lower layer T = 13.5 ° C, ρ = 1.0754 g / cm ³ , C = 72.5%. From the equality of parameters it follows that the homogeneity of the solution is achieved. After that, the solution is adjusted by introducing 165 kg of water and mixing by circulation with bubbling for 10 minutes. The final solution has a mass fraction of acetic acid of 70.26%.

Example 2

The experiment is carried out analogously to example 1, but create a mass fraction of acetic acid in the water cushion 34.5%. In this case, there is also no mixing of the water cushion with the initial solution, since after the second filling of the container with the feedstock, C = 34.3% in the upper layer. In this case, the circulation time with bubbling is extended to 15 minutes.

Example 3

A mass fraction of acetic acid in the water cushion is 26.3%. In this case, there is also no mixing of the water pad with the original solution. After the second filling of the tank, C = 25.41% in the upper layer. In this case, the circulation time with bubbling is extended to 25 minutes.

Example 4

The experiment is carried out analogously to example 1, but the concentration of the water cushion is 57.3%, i.e. more than 55%. In this case, the water pad is mixed with the stock solution. This can be seen from the analysis of the upper layer after the second filling operation ρ = 1.0777 g / cm ³ and C = 73.4%.

Example 5

Acetic acid with a mass fraction of the main substance of 80% is used as a feedstock. Create a water cushion with a concentration of 13.2%. It is saved during the second filling. Thus, to create a mass fraction of acetic acid in a water cushion of less than 20%, a higher mass fraction of acetic acid in the feedstock is required, and an aqueous solution of acetic acid with a mass fraction of more than 80% is a flammable liquid.

The volume of the water cushion 15-30% of the volume of the pressure vessel is associated with the mass fraction of acetic acid in the feedstock 72-80%.

The advantages of the invention in comparison with the known are the following:

- reduction of fire hazard and toxicity of the process due to the creation of a water cushion with a concentration of 20-55% when acetic acid is in monomeric form, which leads to the absence of low partial pressure of acetic acid in saturated vapors;

- simplification of the technological scheme due to the lack of the need to seal equipment and install a complex vapor recovery system;

- reduction of expenditure rates of feedstock.

Claims (1)

A method of obtaining an aqueous solution of acetic acid, including the first filling of the pressure vessel with an aqueous solution of acetic acid, mixing the solution by circulation, determining the volume of the obtained solution, temperature, density and mass fraction of acetic acid, the second filling of the pressure vessel with the missing ingredients to obtain the required amount (70 ± 1 )% acetic acid, second mixing of the resulting solution, determination of the volume, temperature, density and mass fraction of acetic acid, in case of deviation I’m from a given one, the product of adjusting the solution by loading water or acetic acid, characterized in that the first filling of the pressure vessel is carried out by introducing the calculated amount of water and acetic acid to obtain a solution of acetic acid with a mass fraction of 20-55% in the amount of 15-30% of the volume of pressure capacity, the second filling is carried out with the initial 72-80% solution of acetic acid to a predetermined volume, the second mixing of the contents of the pressure vessel is carried out by circulation with simultaneous bubbling of dissimilar alignment via air leaks into said container for 5-30 minutes, adjusting the solution to determine the density, temperature and mass fraction of acetic acid in the upper and lower layers in case of non-homogeneity of the solution was repeated by bubbling stirring operation.