DMF(N,N-dimethylformamide) is widely used in PU leather, acrylic fiber spinning and pharmaceutical intermediate industries. DMF in waste liquid is miscible with water and has a boiling point of about 153 ℃. It can neither stand and separate water like a solvent insoluble in water, nor can it directly recover high-concentration products by simple condensation. The recovery of DMF takes the rectification route. The core contradiction is to separate from water. If the separation route is selected in the right way, the quality and cost of the recovered liquid can be controlled, and the disposal burden of waste liquid will also become the reflux of raw materials.
The composition of DMF waste liquid varies greatly from industry to industry: PU leather industry solidification tank waste liquid concentration is high, containing a small amount of additives; Spinning industry waste liquid contains salt and oligomers; Pharmaceutical industry waste liquid is often mixed with other solvents and impurities. The common point is that the water content is high and the boiling point difference with water is suitable-distillation separation is feasible. Suspended solids and salts in the waste liquid are hidden dangers of distillation. The fouling and corrosion of the tower can be controlled by removing them before pretreatment. The feed quality is stable and the operation of the tower is stable.
The conventional route is pretreatment and rectification: the waste liquid is first filtered to remove impurities, and then separated into a rectification tower-water is distilled from the top of the tower, and DMF is collected from the bottom of the tower. The bottom temperature of the tower is calculated according to the decompression condition. The boiling point of DMF under normal pressure exceeds 150 ℃. The decompression distillation reduces the operating temperature, benefiting both heat sensitivity and energy consumption. For waste liquid containing acid or impurities, pretreatment increases neutralization and light removal steps. The purity and moisture of the recovered liquid are tested by batch, and the reuse grade is determined according to the test results. The ledger records the whereabouts of each batch. The operating parameters of the tower are set at one time when it is put into operation: the feed temperature, reflux ratio and liquid level at the bottom of the tower correspond to the product quality, and the corresponding relationship between the parameters and the detection data is recorded during operation, and the rules can be found after several batches. When the feed component changes greatly, the ledger collected in different stages is connected with the feed schedule of the tower, and the load of the tower is stable and the unit energy consumption is low.
The water phase distilled from the top of the tower contains a small amount of DMF, which is inappropriate for direct discharge. The conventional method is dilute liquid recovery: dilute DMF aqueous solution is concentrated by azeotropic distillation or extraction, and DMF is recovered. The treated wastewater enters the sewage system for disposal according to specifications. The input and output of dilute liquid concentration should be accounted for: dilute liquid concentration with too low concentration has high concentration cost, and it should be treated according to concentration in stages-direct distillation of concentrated waste liquid, distillation after concentration with medium concentration, dilute liquid should be used in processes that are not sensitive to concentration, and the treatment cost can only be pressed down.
| Segment | Features | Configuration considerations |
|---|---|---|
| Source of liquid waste | Large industry differences | Sub-concentration and file collection |
| Preprocessing | suspended matter salinity | Filtration and desalination first |
| distillation | Boiling point 153 ℃ | Decompression operation control bottom temperature |
| overhead water phase | Contains a small amount of DMF | Dilute liquid concentration co-ordination |
| Recovery liquid | Grade according to purpose | Batch-by-batch inspection and sub-use |
| Energy consumption | Distillation consumes large energy | heat integration consumption reduction |
Look at the impurity spectrum. Coagulation tank reuse is the most tolerant of impurities, and can be directly rematched after passing the test. Spinning and medical use are sensitive to impurities, which are treated according to the grade of use, checked batch by batch, and degraded for unqualified use.
Pretreatment and desalination are given priority to: filtration and desalination are the first steps. Direct entry of salt-containing waste liquid into the tower will accelerate scaling and corrosion. The cost of tower damage treatment is higher, and the money for pretreatment cannot be saved.
Decompression and bottom temperature reduction, heat integration and preheating of feed, and utilization of waste heat at the top of the tower will be started. Before the transformation, energy consumption tests will be done first, and the accounts will be settled before the operation will be started, so as to avoid changing the place but not saving money.
This article by LuoyangWohong PetrochemicalEquipment Co., Ltd. arranges that the company provides design, manufacturing and operation and maintenance services for condensation recovery, membrane separation recovery and complete solvent recovery devices for chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please contact and exchange.
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