Method for recovering dimethyl formamide

Abstract

A method for recycling dimethyl formamide relates to a method for recovering dimethyl formamide from waste water by an all-subpressure operation method. The method includes the steps of utilizing conduction oil or low-pressure steam as a heat source, sequentially leading the waste water containing DMF to four subpressure operation towers, and performing subpressure concentration in the first tower and the second tower, subpressure fractionating in the third tower and deacidification in the fourth tower, thereby obtaining finished DMF and methanoic acid. Due to the great decrease of stable operating temperature, the recovery rate of the DMF can reach over 99 percent, and the rate of purity reaches 99.99 percent; the resolution ratio of the DMF and the back evaporation rate of the peracid DMF are obviously reduced, a methanoic acid decomposition tower is cancelled, almost no DMF contains peracid, repeated rectification is not needed, and energy sources are saved by over 10 percent; and meanwhile, the dimethylamine quantity generated by decomposition is little and is completely absorbed by a boiler screen dust collection system without emission.

Description

technical field [0001] The invention relates to a method for reclaiming dimethylformamide from waste water, in particular to a method for reclaiming dimethylformamide from waste water using a full negative pressure operation method. Background technique [0002] Before the present invention was proposed, many domestic synthetic leather factories, acrylic fiber factories, and glove factories used dimethylformamide (abbreviation: DMF, the same below) as a solvent for batching in the production process. In order to reduce production costs, protect the environment, and protect people's health, these production plants have set up recycling devices to recycle DMF for reuse. There are also many equipment manufacturers who have finalized the production of recovery devices and provided them to the production plants. Generally speaking, most of these devices are four-tower processes, that is, the recovered waste water is first vacuum concentrated in the first and second towers to rem...

AI Technical Summary

Problems solved by technology

This type of device uses heat transfer oil or low-pressure steam as a heat source, and the degree of heat energy reuse is not high

Atmospheric pressure rectification is adopted in the device. In the presence of water, when the temperature reaches 120-130°C, DMF is very easy to produce DMF and formic acid, and DMF and formic acid will produce azeotropy. After passing through the four-tower negative pressure deacidification tower The content of DMF in the final formic acid is still very high and must enter the formic acid decomposition tower for partial decomposition, and then return to the rectification tower for repeated rectification through alkali neutralization, which is a great waste of energy

In addition, DMF decomposes dimethylamine, although it can go through the deamination tower and then enter the boiler water curtain to remove dust and neutralize the acidic water, but due to the large amount of decomposition, the dimethylamine cannot be completely neutralized and pollutes the environment. In the four-tower recovery unit, the yield of finished products is less than 95%

Although many places have modified the four-tower recovery device, such as increasing the number of recovery towers to five or six towers (that is, adding formic acid decomposition towers and steam deamination towers), or even transforming the four-tower recovery into three-tower recovery, in terms of energy It can be saved in utilization, but the rectification at atmospheric pressure and high temperature promotes the decomposition of DMF, and still cannot solve the two major problems of low recovery rate of DMF and environmental pollution.

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