Styrene is the core monomer of polystyrene, resin and rubber industry. Its boiling point is about 145 ℃. From the boiling point point, it is a "good recovery" object of condensation recovery-the temperature level requirement is loose, and the big head can be recovered by water cooling at normal temperature. But styrene has a property that cannot be bypassed: it is easy to self-polymerize. The increase of temperature, the extension of residence time and the entry of impurity will make the styrene in the condensate polymerize slowly, and the heat release of polymerization will accelerate its own trend. So the recovery of styrene configuration, half of the mind in the condensation, half of the mind in the anti poly.
In the production of polystyrene and resin, styrene tail gas comes from the exhaust of polymerization reaction, devolatilization process, tank breathing and preparation filling. The exhaust of the polymerization kettle fluctuates with the reaction stage, the concentration of the devolatilized exhaust gas is high and the temperature is high, and the respiration of the storage tank fluctuates with the temperature difference between loading and unloading and day and night. The temperature and concentration of each gas are different, and the collection is divided into manifold: the high-temperature gas is cooled first and then remitted, and the breathing of the storage tank is set up separately, so that the feeding conditions of the treatment section are stable.
The odor threshold of styrene is low, and the trace leakage is obviously perceived. The sealing and negative pressure maintenance of the collection system are more concerned than the general solvent.
The condensing section is designed according to the boiling range of styrene, and the main recovery can be completed by two stages of water cooling. The loose temperature is the advantage of this system. Configuration to control three parameters: temperature, residence time and cleanliness. The temperature on the condensate side is controlled within the range that does not trigger obvious polymerization. The shorter the residence time of the condensate on the heat exchange surface and in the liquid collecting tank, the better. The capacity of the liquid collecting tank is matched according to the rhythm of "timely delivery", and the large tank is not used for slow storage. The heat transfer surface remains smooth, and once the polymer hangs on the surface, the deterioration of heat transfer and the acceleration of polymerization will push each other.
It is a common practice in the industry to add an appropriate amount of polymerization inhibitor to the condensate. The type of polymerization inhibitor and the replenishment period are determined according to the polymerization characteristics of the material. The concentration of polymerization inhibitor in the condensate is included in the test items.
Anti-aggregation is a systematic project, and the whole chain has actions from collection to reuse: the collection pipeline avoids high-temperature dead corners, the slope and drainage are in place, and condensate is not allowed to stay at low points; The heat exchange surface shall be checked and cleaned regularly, and the cleaning period shall be determined according to the condensate state instead of the calendar. The condensate flows with collection and circulation, and connects smoothly with the downstream reuse process. The intermediate storage tank is only for buffering but not storage; temperature monitoring points are distributed at key positions on the condensate side, and temperature trend abnormalities occur before polymerization, allowing time for disposal.
| Segment | Risk point | Anti-aggregation measures |
|---|---|---|
| Collection line | Condensate retention dead angle | Slope drainage not retained |
| Condensation section | Heat exchange surface polymeric wall-hanging | Regular inspection and cleaning |
| Condensate temperature | high temperature accelerated polymerization | The temperature level is controlled in the anti-aggregation zone |
| Liquid collecting tank | Long residence time | Small tank buffer timely delivery |
| polymerization inhibitor | Insufficient concentration failure | Add batch-by-batch inspection as per cycle |
| Recoil end | polymer feed system | Purity and polymer double inspection |
The recovered styrene is classified according to purity and inhibitor content: those with up-to-standard purity and appropriate inhibitor content are directly reused for production, and those with slightly lower purity are degraded for use or recycled for refining. In addition to the conventional moisture and purity of the testing items, the polymer content is a unique indicator of styrene, which is tested batch by batch and disposed of separately to prevent the polymer from entering the production system.
There is risk. Styrene in the condensate will also polymerize slowly at room temperature, faster when the temperature is high and the inhibitor is insufficient. According to the rhythm of "receiving and turning", only buffer is set in the middle without long-term storage. When storage is inevitable, the polymerization inhibitor is supplemented and the polymer content is monitored.
The combination of polymer and metal surface is strong, the conventional solvent cleaning effect is limited, and the thermal cleaning or mechanical cleaning is used. After cleaning and resuming operation, the condensate state shall be observed in an encrypted manner, and the temperature distribution and flow field shall be checked at the repeatedly occurring parts of the polymerization, so as to slow down the wall-hanging speed from the source.
Purity, moisture, inhibitor content and polymer content are up to standard can be used. Test batch by batch before reuse, the index card is slightly stricter than the purchased raw materials, and the stability of the polymerization batch is much more important than saving a little raw materials.
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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