The method of purification of gas emissions from acrylonitrile

 

The invention concerns a method of cleaning gas emissions from Acrylonitrile. The method consists in the fact that the gases containing the nitrile of acrylic acid, sequentially passed through the apparatus with activated charcoal and bioabsorbable with a nozzle, which is irrigated with an aqueous suspension of the biocatalyst-based strains producing enzyme nitrilimines. The invention allows the cleaning of gases from the nitrile of acrylic acid in a wide range of concentrations at low costs biocatalyst without special regeneration of coal during operation of the treatment plant. 2 C.p. f-crystals, 3 tab., 1 Il.

The invention relates to biotechnology and relates to a method for treatment of gas emissions from the nitrile of acrylic acid (EAA), which is used in biotechnological method of producing acrylamide by using a biocatalyst.

Known catalytic, chemical and sorption removal of the NAC from the gas phase.

The first group includes methods related to the catalytic oxidation of NAC. These processes take place at high temperature, which is a significant disadvantage. Thus, the palladium catalyst MA-15 effective when teachaway complete cleaning gas emissions from NAC at a temperature of 160o[2]. Industries associated with the processing of plastics, the application of this method is justified by the fact that the formed gas emissions contain small amounts of NAC (not more than 1 mg/m3along with other volatile monomers that undergo complete oxidation. The use of catalytic oxidation of NAC in conditions when its content in the exhaust gases is large, it is inefficient because it leads to the destruction of valuable raw materials.

Chemical methods of decontamination NAC characterized by the use of large amounts of adsorbent (the further processing of which is the problem), loss of large quantities of nitrile, the advent of highly toxic reaction products. So, if removing the NAC from the gas phase of the cooled 4-7% sodium hydroxide solution [3] is formed a solution of sodium acrylate, which can be used when burning waste NAC toxic gases containing hydrogen cyanide and nitrogen oxides in concentrations of 0.7-4 mg/m3[4].

Sorption methods of trapping NAC based on its absorption of solid porous materials (e.g., activated carbon) or liquids (usually water) [5] . A General lack marbletown neutralization nitrile of acrylic acid, contained in the gas phase, is a biotechnological method based on the enzymatic hydrolysis of the nitrile. As described in the patent of the Russian Federation 2138322 [6], NAK from the gas phase is absorbed (first in the trap, and then in a Packed absorber) suspension cells of strains of Rhodococcus rhodochrous M8 or Rhodococcus rhodochrous M33. These strains catalyse the conversion of Acrylonitrile to acrylamide, which is a non-volatile compound. The process is economical, runs at normal temperatures and is characterized by high efficiency at relatively low water consumption. Furthermore, formed in the process of cleaning solution of acrylamide containing waste sludge biocatalyst, is used as raw material in the production of polyacrylamide.

As follows from the description, the process provides a high degree of purification of gases from the NAC at concentrations of 10-200 mg/m3, however, requires excessively high costs of catalyst (3 g/l by dry weight). In addition, the treatment system proposed in this invention, provides for the presence of ineffective trap-bubbler with the suspension of the biocatalyst. Thirdly, to ensure acceptable concentrations of nitrile at the outlet of the treatment plant if the peak is and for irrigation of the absorber. This measure will have a positive effect only up to a certain limit, determined by the absorber. Deep cleaning of gases from NAC in such situations will require increasing the capacity of the treatment plant.

The present invention aims at improving the efficiency of gas purification from NAC in a wide range of concentrations of NAC (up to thousands of mg/m3with simultaneous reduction of the expenditure of the biocatalyst.

The method is as follows.

Gases containing NAC, sequentially passed through the adsorption apparatus with activated charcoal and bioabsorbable with a nozzle, which is irrigated with an aqueous suspension of the biocatalyst-based strains producing the enzyme nitrilimines - Rhodococcus rhodochrous M8 or Rhodococcus rhodochrous M33.

Cleaning is subjected to gas emission concentration of NAC to 1500 mg/m3(1-1500 mg/m3). It is advisable to use the biocatalyst described above, in the form of a suspension with a concentration of not more than 0.02% by weight of dry cells.

These differences can intensify the process and to reduce the amount of biocatalyst.

Schematic diagram of the treatment plant shown in the drawing, where 1 - damper with activated coal the new coal performs the function of damper, reducing the extremely high concentrations of NAC in the cleaned gases by adsorption. Subsequently NAC gradually desorbed and transported with the gas stream in bioabsorbable. The duration of the desorption NAC absorbed during its peak, significantly exceeds the duration of the emission. Periods emissions rare and relatively short, so the concentration of NAA in the gases at the outlet of the adsorber will always be lower than the input peak concentrations, and after some time will be close to the values common to the production. This gives you the opportunity to make the operation of the biological treatment unit is more effective at a much lower cost of the biocatalyst. In addition, sorption and desorption of NAC in the damping apparatus occur during operation of the treatment plant, so special regeneration of the coal will not be required, and this significantly reduces the complexity of the method and simplifies the technology.

The proposed method is illustrated by examples.

In all the examples, the mixture of vapor NAC with air is formed due to the evaporation of NAC in a stream of air at room temperature. The air flow rate was 2.0-2.8 km DM3/min. Concentration IN the absorber, which is a glass column with a height of 52 cm and an inner diameter of 2.5 cm, with two sections of the nozzle height 13 cm, separators for the separation of gas and liquid flows and liquid distributors. The nozzle consisted of scraps of glass tubes with a diameter of 6 mm, a length of 6-10 mm with wall thickness 1 mm cell Suspension of strains-producers of nitrilimines (0.02 mass% of dry cells) was applied to the upper part of the column at a constant speed. The initial volume of the suspension was 80 cm3. As strains with nitrilgidrataznoi activity, were used strains of Rhodococcus rhodochrous M8 and Rhodococcus rhodochrous M33.

The damper was a vertically located a glass tube of internal diameter of 1.6 cm, closed at both ends by plugs with taps. The coal layer was sandwiched between cotton swabs.

Example 1 the Mode of operation of the treatment plant without damper.

At the entrance of the absorber, without the use of a damper, bottom pull air containing vapors of NAC in different concentrations. The content of NAC in the air was determined at the inlet and outlet of the absorber. The results are presented in table. 1.

Example 2 the Mode of operation of the treatment plant with the damper.

Before the absorber was installed damper, sod the p>3. The air containing a pair of NAC was applied to the input of the damper within an hour (mass NAC 0,160 g), and then fed clean air. The air outlet damper arrived at the entrance of the absorber. The content of NAC in the air was determined at the inlet damper at the inlet and outlet of the absorber. The results are presented in table.2.

According to the data given in table. 1 and 2, in the absence of the damper (PL. 1) input concentration of NAC 1430 mg/m3corresponds to the concentration of NAC output bioabsorbable 27 mg/m3. In the presence of the damper when filing within one hour air with NAC 1500 mg/m3the highest concentration of nitrile at the entrance of the absorber was only 154 mg/m3(1/10 largest source), and the output is 1.4-1.5 mg/m3.

Example 3 this example demonstrates the ability of the different grades of activated carbons for adsorption of NAC.

The damper was put on to 5.00 g of activated carbon of various brands. To the input of the damper within 30 minutes was applied with a current of air 0,080 g (NAC average concentration of NAC at the entrance 1100 mg/m3), and then blew coal air. Measured concentrations of NAC output. The results are presented in table.3.

From the data presented in table.3, it follows that the coal grades BAU-a and AG-5 is no barbirolli NAC: the maximum concentration of NAC at the output of the damper was observed respectively after 30 and 45 min after the start of the filing of the NAC. It should be noted that the coals of these brands had granules of a larger size than the coal grades BAU-a and AG-5, resulting in a layer of these adsorbents were large void that led to the breakthrough of the NAC through the damper. In a special experiment, where the granules of coal AR-were previously fragmented into smaller particles, with the highest concentration of NAC at the output of the damper was 72 mg/m3(compared to 524 mg/m3in the case of intact granules). Therefore, for use in industrial water treatment facility may use the coal we tested all brands with a suitable choice of the height of the layer of adsorbent, preventing leakage of NAC.

References 1. Catalytic oxidation of gas emissions from the production of Acrylonitrile. / Ie Petkevich, E. F. Ivankovic, C. N. Makaton etc. // proceedings of IV all-Union conference "Catalytic purification of gases. Alma-ATA: Nauka, 1988. - S. 7.

2. Design and model tests of a method of catalytic gas purification from the impurity of Acrylonitrile. / C. M. Vlasenko, S. A. Solovyov, M. Beloglazova etc. //Chemical industry. -1992, 5. - S. 17-19.

3. Pat. GDR 2003134, class B 01 D 53/14, 1981.

4. Hygienic assessment of the effectiveness of fire neutralization theopro labour hygiene and occupational pathology in some sectors of the chemical industry and road transport. - M., 1981. -S. 16-19.

5. Lame B. S., Agrees F. I. the Development of an optimal method of neutralizing free nitrile of acrylic acid. // The production and use of elastomers. - 1992, 11. - N-3-10.

6. RF patent 2138322, class B 01 D 53/04, B 01 D 53/84, C 12 P 13/02, 1999.

Claims

1. The method of purification of gas emissions from the nitrile of acrylic acid (EAA), characterized in that it envisages that the gas emissions containing NAC, previously passed through the apparatus with activated carbon, causing dangererous effect, and then through bioabsorbable with a nozzle containing a biocatalyst-based strains of Rhodococcus rhodochrous M8 or Rhodococcus rhodochrous M33.

2. The method according to p. 1, characterized in that the purification is subjected to gas emission concentration of NAC 1-1500 mg/m3.

3. The method according to p. 1, characterized in that the use of biocatalyst on the basis of these strains in suspension with a concentration of not more than 0.02% by weight of dry cells.

 

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