Treatment of wastewater containing DMF

It can be processed through distillation: most of the water is removed by initial evaporation, which results in the formation of fine salt crystals; the salt is then filtered out, and the filtrate is distilled to obtain pure DMF.

1. Coarse distillation is no problem; using a distillation column of a few theoretical plates results in water that contains almost no DMF. I just checked the literature; the solubility of sodium chloride and sodium sulfate in pure DMF is almost zero. Therefore, as the DMF concentration increases, two liquid phases will definitely form at the bottom of the tower; the organic phase can be directly extracted from the distillation tower to remove water, while the crude DMF at the bottom of the tower still contains some salts, and it needs to undergo simple evaporation to produce a purer DMF product. Ultimately, the salt concentration in the aqueous phase can exceed 25%, with very little DMF present; it is best to be able to reuse it. Otherwise, evaporation crystallization (rather than cooling crystallization, noting that the solubility of sodium chloride hardly changes with temperature) is required to obtain the solid salt mixture. Throughout the entire process, approximately 1.2 to 2 tons of steam at a temperature of over 170 degrees are required to treat 1 ton of wastewater (the boiling point of DMF at atmospheric pressure is around 155 degrees). The energy consumption is still quite high. 2. If (negative pressure) multi-effect (3–6 effect) evaporation is used in place of simple evaporation, high-temperature steam can be saved; however, the resulting liquid is still impure and contains about 1–2% DMF, which requires further treatment. 3. The thermally driven membrane separation process we have developed has unique advantages if used to concentrate such wastewater in place of rough distillation. The waste heat from the aforementioned DMF-water distillation column (the 100-degree condensed water at the top of the column and the hot DMF at 155 degrees at the bottom) can almost provide the driving force for the heat-membrane process we recommend. In this way, the energy consumption for the entire process is 0.3–0.4 tons of steam per cubic meter of wastewater. This process is generally used to concentrate various saline solutions to high concentrations and recover fresh water. This process does not require high temperature, high pressure, or negative pressure (or vacuum) to operate. This process can use a low-temperature heat source (60–100 degrees) as a driving force, but its heat efficiency (measured by the water production ratio) is much better than that of multi-effect evaporation (with 20 effects or fewer). The electrolyte concentration in the fresh water produced by this process can be as low as less than 1 ppm, with typical values ranging from 10 to 100 ppm. Another feature of this process is that the equipment used is mostly made of plastic, which completely eliminates the corrosion problem associated with multi-effect evaporation. As mentioned earlier, even in the absence of high temperature and pressure or negative pressure (or vacuum), the heat utilization efficiency of this process remains better than that of multi-effect evaporation. For example, the water production ratio for this process is generally between 8 and 12, whereas that for 6-effect evaporation is usually below 4.5. Of course, a small amount of DMF will still end up in the distilled water. However, the membrane itself provides an additional factor of two in DMF/water selectivity on top of the gas-liquid equilibrium, so the DMF content in the effluent is much lower compared to that using multi-effect evaporation. With segmented water discharge, a portion of the wastewater with a higher DMF concentration can be combined with the original wastewater, without affecting the economic efficiency of the entire process. If you are interested in our process, please contact yjqin1@yahoo.com or yqin@chembrane.com. This post was last edited by johncom on 2009-4-8 08:16.]

Study! Recovering DMF from low-concentration DMF aqueous solutions is rather troublesome, especially in the presence of inorganic salts. Membrane separation technology is something that could be considered, but I’m not sure how its operating costs compare to those of distillation Additionally, choosing an appropriate extractant (with a low boiling point and low vaporization latent heat) to extract DMF from water, and then distilling the organic phase to recover the extractant and DMF, is also a method that can be considered.

“Membrane separation technology is something that could be considered, but I’m not sure how its operating costs compare to those of distillation ” To evaporate one ton of water using a distillation tower, 140–160 degrees of steam is required, which amounts to more than 1.2 tons ； To produce one ton of water using a membrane-based multi-stage multi-effect evaporation system, 100 degrees of steam is required

Use evaporation concentration or freeze crystallization processes!

Distillation is a viable method; by performing fractional distillation based on the different boiling points of various substances, it is possible to recover products with high purity. In this regard, those with expertise in the chemical industry are more skilled.

Ion liquid extraction can be considered.

The low boiling point and low heat of vaporization of the extractants trichloromethane or dichloroethane can be utilized to first extract and then distill DMF from wastewater for recovery

Direct distillation may require a high amount of energy; perhaps it would be possible to use the extractant chloroform to first extract and concentrate DMF, and then carry out distillation to obtain DMF of higher purity, with chloroform being able to be recovered through distillation for reuse in extraction. Previously, we carried out industrial production of DMF and chloroform via the coproduction of chloro-oil and dimethylamine, and chloroform was used as an extractant for the recovery of DMF from the reaction mixture.

The method upstairs is good, and 5% sodium chloride along with other salts also have a salting-out effect.