Treatment of acrylonitrile exhaust gases
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In one engineering design, acrylonitrile is used as both a solvent and a reactant; the reaction products are separated by centrifugation (under nitrogen protection), and the exhaust gas generated (at a flow rate of 50 cubic meters per hour and at a temperature of 10 degrees) is cooled to 0 degrees using an exhaust condenser； Acrylonitrile is recovered through vacuum distillation of the mother liquor. The distillation process features two stages of condensation, with the condensate temperature at 0 degrees. The vacuum pump is a Siemens water-ring type, with a water discharge rate of 1.2 cubic meters per hour at room temperature; its gas extraction capacity is 500 standard cubic meters per hour. The exhaust gas from the vacuum pump is discharged directly outside. Due to the high saturated vapor pressure of acrylonitrile at 0 degrees, the emission rate exceeds the specified limits. Could those of you with experience in this field provide some solutions? Preferably, examples of successful engineering implementations would be useful. Thank you!
The exhaust gas from the vacuum pump can be absorbed directly using ethylene glycol (which may be too viscous at low temperatures), or using DMF, DMAC, or NMP; pure acrylonitrile can be obtained through distillation. Its absorption by water is somewhat poor, and there are azeotrope problems during distillation. How to handle acrylonitrile in the drainage from vacuum pumps?
The mother liquor contains virtually no water; during vacuum distillation, only acrylonitrile is extracted for reuse. The acrylonitrile content in the wastewater discharged from the vacuum pump should be around 8% (due to the solubility of acrylonitrile in water and minor amounts carried along). It is planned to use chlorine dioxide for oxidative degradation before discharging the wastewater, so that it can meet the required standards after further treatment.
The acrylonitrile content in the wastewater discharged by the vacuum pump should be around 8%, with a wastewater flow rate of 1.2 tons per day. 0.2 tons of acrylonitrile are lost every day, which results in a high consumption of chlorine dioxide. Can chlorine dioxide oxidize acrylonitrile into nitrogen? Otherwise, removing ammonia from the wastewater is another problem. The biochemical treatment of acrylonitrile is very difficult, as the required concentration in the effluent must be extremely low; this represents a major challenge for acrylic fiber factories. I still recommend using a distillation system to recover acrylonitrile from the wastewater.
Due to the low volume of water, it is feasible to treat the wastewater by oxidizing it with chlorine dioxide and then discharging it. Even for ammonia nitrogen, as its total amount is low, its concentration in the wastewater remains within controllable levels, allowing the use of the A/O process for nitrogen removal. It’s more convenient this way.
We used to treat the cyanide-containing wastewater generated by one of our products with chlorine dioxide; of course, this method was quite costly. Additionally, acrylonitrile tends to polymerize on its own in water; whether it has any value for recycling can only be determined after analyzing the water sample and comparing the costs of the two options.
May I ask the poster, what are your products? Where? I don’t have a solution for treating acrylonitrile waste gas, but I do have some suggestions regarding the control pumps.
Our unit is also looking for good solutions regarding the venting of the large tanks.
Our company handles the treatment of acrylonitrile exhaust gases in China; please send me a message if you have any questions.
Is it again Donghua Company from upstairs, here to promote your catalytic incineration?