How do the vapor pressure and boiling point of solvents affect the recovery method? In summary, solvents with high vapor pressure and low boiling point evaporate in large quantities at room temperature, with multiple emission points and dispersed concentrations. Condensation requires a very low temperature to be contained; Solvents with low vapor pressure and high boiling point are quiet at room temperature, and their emissions are concentrated in high-temperature processes. They are easy to collect and have mild condensation. These two indicators are two sides of the same thing - boiling point is the temperature at which the vapor pressure equals the external pressure. Before selecting the recovery method, check them carefully, and the configuration will be half successful.
The vapor pressure describes the "momentum" of a liquid emitting vapor at a certain temperature, with higher temperatures leading to greater vapor pressure; When the vapor pressure rises to equal the external atmospheric pressure, the liquid boils, and the corresponding temperature is the boiling point. So varieties with low boiling points have a higher vapor pressure at room temperature. Ether has a boiling point of about 35 ℃ and ethyl acetate has a boiling point of about 77 ℃. You can smell a clear odor at room temperature even with an open mouth. That's the reason.
The emission of low vapor pressure solvents is ubiquitous: breathing at room temperature storage tanks, open feeding, cleaning operations, painting and drying are all sources, and the collection system should be organized according to "multi-point, low concentration, and high air volume"; The emission of high vapor pressure (high boiling point) solvents is concentrated in the heating stage: the tail gas from distillation, drying, and high-temperature reactions is the main source, and the loss in the storage and transportation at room temperature is limited. Therefore, the collection can be arranged with a focus on "few points, high concentration". The order of judgment is to first determine the process temperature, and then look at the storage and transportation room temperature.
The amount that can be condensed depends on the difference between the partial pressure of the vapor in the exhaust gas and the saturated vapor pressure of the solvent at the condensation temperature. Low boiling point solvents have a high saturation vapor pressure at room temperature, and the condensation temperature needs to be pressed very low to allow most of the vapor to condense. The refrigerant level and insulation and frost prevention should also keep up; High boiling point solvents can achieve high recovery rates at mild condensation temperatures, with low energy consumption and frost risk. The configuration differences of different boiling point ranges are shown in the following table:
| Boiling point range | Emission characteristics | Key points for recycling configuration |
|---|---|---|
| Low boiling point (below about 80 ℃) | Volatile at room temperature, dispersed with high concentration | Priority should be given to closed collection, with deep freezing and multi-stage addition |
| Medium boiling point (approximately 80 to 150 ℃) | Room temperature is limited, with a focus on thermal processes | Mainly two-stage condensation, taking into account the ambient temperature branch |
| High boiling point (above approximately 150 ℃) | Concentrate on high-temperature sources such as distillation and drying | High temperature conduit insulation, mild condensation conditions |
One is to only look at the boiling point and not the vapor pressure curve: the vapor pressure of different solvents has different steepness with temperature, and the difference will be amplified when approaching the boiling point, and it is more accurate to check the vapor pressure close to the working temperature. The second is to regard "non-volatile" as "no collection": the concentration of off-gas in the high-temperature process of high-boiling solvents can be very high, and missing these points will lose the big head of recovery. The mixed solvent should also pay attention to the volatile appearance determined by the light components. The component proportion of the recovered condensate will change with time, and the ledger should be tracked by batch.
It can't just boil over. Water solubility, azeotropic behavior with impurities, and thermal stability will change the condensate treatment route, and the recovery schemes for two varieties with similar boiling points may be completely different, which will be determined after item-by-item verification.
The vapor pressure of the mixture is superimposed by the partial pressure of each component, and the light component contributes the bulk, and the overall appearance is close to "light component dominance". The design is based on the condensation requirements of the light components to set the temperature level, the condensate components fluctuate with the batch, before reuse according to the batch test deployment.
The safety technical instructions provided by the solvent supplier are used as the first source, and the process design is rechecked in combination with the measured emission concentration. The vapor pressure of solvents in different batch numbers and water-bearing states will deviate, and the key working conditions shall be subject to the field measurement.
LuoyangWohong PetrochemicalEquipment Co., Ltd. provides solvent volatility assessment, recovery process selection and device design and manufacturing services. Welcome to contact and exchange.
This article is organized by Luoyang wohong petrochemical equipment co., ltd. if you need to evaluate the selection of recycling methods or on-site investigation, please contact and exchange.
Mr. Li 13526990215
Hotline
