Dipropylene glycol methyl ether is a high boiling point ether alcohol solvent commonly used in coating, printing ink and cleaning agent industry. Its boiling point is about 190 ℃, and it is completely miscible with water. The main line of its recovery is "closed collection + main amount of condensation collection + distillation dehydration reuse": the burden of the condensation link itself is not heavy, the real difficulty lies in the mutual solubility of the recovered liquid and water, and the ineffectiveness of static stratification. Distillation or rectification dehydration must be arranged, which should be clearly thought out from the beginning of selection.
The first is a high boiling point. The boiling point of about 190 ℃ means that the volatilization at normal temperature is limited, and the emission is concentrated in high-temperature processes such as drying and high-temperature cleaning: when the temperature goes up, a large amount of vapor enters the gas phase, and the concentration of exhaust gas fluctuates obviously with the working conditions. The collection system should be designed according to the most unfavorable working conditions.
The second is miscible with water. Ether alcohols have strong hydrophilicity, and the condensed recovered liquid cannot be left standing and stratified like esters and aromatic hydrocarbons, and dehydration must rely on distillation. This also means that once running, dripping and leaking into waste water, the separation is equally difficult, and the recovery link must be collected.
The third is combustible. The exhaust system shall be selected for fan selection, electrical explosion-proof and anti-static grounding according to combustible medium, and shall not be relaxed due to slow volatilization at normal temperature.
The high-temperature process branch is led out separately and cooled before it is imported into the main pipe. Vacuum pump and drying furnace exhaust are connected to the condensing unit nearby to avoid liquid accumulation during long-distance transportation. The normal temperature open operation point shall be locally enclosed and directional exhaust. Keep the slope of the pipeline, set a low point to drain the liquid and purge it regularly-the condensation residue of high boiling point varieties on the pipe wall is more obvious than that of low boiling point varieties, and the drain point should be set denser.
High boiling point varieties can condense most of the main volume by water cooling at normal temperature, which is less labor-saving than low boiling point varieties. However, high-temperature exhaust gas needs to exchange heat and cool down before entering the condensation section. In the two-stage arrangement, the main amount of normal temperature water in the front stage is collected, and the lower refrigerant temperature in the rear stage is collected. How cold is it and how much is the recovery rate, shall be determined by the measured concentration and recovery rate targets. In the case of strict emission requirements, the adsorption unit is connected to trap the residue after condensation, the adsorbent is desorbed and regenerated periodically, and the desorbed gas is returned to the condensation unit for closed-circuit recovery.
| Recycling route | Applicable scenarios | Configuration considerations |
|---|---|---|
| Single-stage or two-stage condensation | High concentration and stable components | High boiling point condensation is easy, focusing on cooling and reducing load first. |
| Condensation adsorption finishing | Occasions with strict emission requirements | The main amount of condensation is collected, and the residue of the end adsorption pocket is collected. |
| adsorption concentration desorption condensation | Low concentration tail gas with large air volume and low concentration | Concentrate and reduce air volume first, and condense according to small air volume and high concentration |
Solubility with water means that the road of standing and stratification is impassable. Dehydration is directly arranged for distillation: water and light components are removed under normal pressure or reduced pressure according to the difference of distillation range, and the dehydrated crude product is further refined according to purity requirements. Recycling by use-cleaning and dilution can be used after dehydration, and the ingredients sensitive to purity can be refined according to the test data. The ledger records the input volume, recovery volume and dehydration volume on a daily basis. When the recovery volume drops, priority is given to checking the sealing of the collection point, the drift of condensation temperature and the scaling of the heat exchange surface.
It belongs to ether alcohols. Propylene glycol methyl ether has a much lower boiling point (about 120 ℃), volatilizes quickly at normal temperature, and a lower refrigerant temperature should be put into the condensation section. Dipropylene glycol methyl ether has a high boiling point and is easy to condense. The difficulty is transferred to the dehydration of the recovered liquid. Both are miscible with water, dehydration to go distillation.
It's useless. The mutual solubility system cannot separate the interface and directly arrange distillation and dehydration. It is unrealistic to solve the problem by lengthening the standing time.
The main quantity can be collected. The condensation ratio of high boiling point varieties condensed at room temperature is itself high. Whether to add low temperature refrigerant or adsorption unit to the tail section is determined according to the emission requirements and the measured concentration.
The condensation residue on the pipe wall of high boiling point varieties is more obvious than that of low boiling point: the pipeline keeps the slope, the low point drainage is encrypted, and purging is arranged during shutdown to prevent clogging of effusion and concentration accumulation.
This article by LuoyangWohong PetrochemicalEquipment Co., Ltd. arranges that the company provides design, manufacturing and operation and maintenance services for condensation recovery, distillation dehydration and complete solvent recovery devices for the paint, ink and cleaning agent industries. If you need process evaluation or scheme configuration, please contact and exchange.
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