Ethyl acetate is the largest ester solvent in the paint, ink and adhesive industries, and the concentration of exhaust gas discharged from the drying and blending process is high and the recyclable value is large. There is a set of mature methods for the separation and recovery of ester tail gas by membrane, but the physical and chemical properties of esters are different from those of alcohols and ketones-flash point, lower explosive limit and water solubility have their own calibers, and the configuration of pretreatment and recovery side should be adjusted accordingly. Taking ethyl acetate system as an example, this paper makes clear the key points of membrane separation and recovery configuration of ester solvent tail gas according to the process, and the operators of the device that has been put into operation can also check their own configuration.
Ethyl acetate is highly volatile, the lower explosive limit is low, and the concentration of tail gas is generally in a higher range in the drying process. Direct emission not only loses the solvent but also brings double pressure on safety and environmental protection. The mutual solubility of esters and water is limited, which is a good thing on the recovery side-the dehydration load can be greatly reduced after the condensate is layered; However, esters will slowly hydrolyze in humid environment, and acetic acid produced by hydrolysis will also bring corrosion problems. Therefore, the humidity management of exhaust gas is stricter than that of alkane system, and dehumidification before membrane should be done sufficiently.
In the selection of membrane layer, the solubility of ethyl acetate to the rubber separation layer is high, the membrane transmission speed is fast, and the enrichment ratio of the single-stage membrane unit is ideal. There are three main points of configuration: the filtration and dehumidification section before the membrane is normally put into operation, the humidity is controlled below dew point, and ester hydrolysis and membrane surface condensate are prevented; The booster equipment is selected according to the explosion-proof partition. The enriched gas on the permeable side enters into condensation and liquefaction, the condensate is standing and stratified, the ester layer is dehydrated and reused, and the water layer is discharged into the sewage system for treatment. The whole process is closed-circuit, the discharge side meets the standard, the recovered solvent is returned to the production line, and the book can stand.
The recovered ethyl acetate should be reused, and the purity index should be tested batch by batch: moisture, acidity and purity are the main three items, which should be reused after refining. A small amount of ester taken away by the layered water phase should be accounted for in loss; when rematching, the purity requirements are graded according to the process caliber-the coating grade and the adhesive grade are separated to avoid cross-affecting product quality. The ledger records the recovery volume, detection value and whereabouts by batch, and the audit and internal traceability are well documented.
There is another experience in the ethyl acetate system: the volume of the stratified tank on the recovery side is fully matched according to the batch output, and the standing time is sufficient. The stratified quality directly determines the subsequent dehydration load; The discharged water phase does not rush into the sewage system, and the surface floating ester is recovered first. The solvent collected over one shift is not a decimal in one year. The recovered economic account is a detail account, which is saved on the process node.
| Segment | key points | Consider |
|---|---|---|
| pre-treatment of membrane | Filtration plus dehumidification | Anti-Ester Hydrolysis and Membrane Surface Condensate |
| Boosting | Selection according to explosion-proof partition | Security level matching |
| membrane unit | Rubber separation layer | High solubility of esters |
| condensation liquefaction | enrichment gas liquefaction | Temperature level according to concentration |
| layered dehydration | Static stratification | Reduce dehydration load |
| Return allocation management | Batch-by-batch inspection | moisture acidity purity three |
Not recommended. The condensation of water and condensate on the membrane surface affects the separation performance, and esters will slowly hydrolyze when they meet water. A dehumidification section is set in front of the membrane to press down the dew point. The input of this section is exchanged for the double insurance of membrane life and recovery quality.
After layered dehydration and simple refining, most batches can reach the target of back matching. Batch by batch detection of moisture, acidity and purity, not up to the standard into the refining process. Before reuse, the purity caliber shall be confirmed with the process, and the grading shall not be crossed.
If the components are compatible and the reuse caliber is consistent, it can be mixed, and the ledger records the whereabouts of each stock separately; The conflict of reuse indicators is collected in groups, and the membrane segment is calibrated according to the dominant component.
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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