Process improvement of polyphenylene sulfide pps desalination, purification, filtration, washing and drying

2023/03/25

Polyphenylene sulfide (PPS) is a high-performance thermoplastic engineering resin. It has excellent high temperature resistance, corrosion resistance, high strength and excellent product stability. It has a wide range of applications in aerospace, automotive, electronics, precision instruments, etc. The application of PPS has become the "sixth largest engineering plastic" and "the first largest special engineering plastic". The industrial synthesis of PPS mainly adopts the sodium sulfide method, which has high synthesis yield, good effect, strong repeatability and simple operation, but The oligomers and by-product sodium chloride generated during the synthesis process and the inorganic additives used in the synthesis process make the PPS product contain more impurities and increase the ash content, resulting in a decline in its comprehensive performance and limited application range. Foreign countries have blocked key technologies such as purification and post-treatment in the PPS synthesis process, making it impossible to produce PPS resins with comparable performance to foreign countries.



PPS is insoluble in any organic solvent below 200 °C, and metal ions inevitably remain in the PPS matrix during the purification process of PPS. In addition to inorganic salts, low-molecular organic salts are also the main form of metal impurities in PPS.

If there are too many oligomers in fiber-grade PPS, more vapors will be produced after melting, resulting in easy filament breakage during spinning, and its fiber strength is low, hairiness is high, toughness is poor, rigidity and strength are insufficient, and the service life of the product is shortened. short. Purification is a process to eliminate impurities and oligomers in the PPS synthesis process, and it is a very critical step in post-processing, which determines the content of inorganic ash and oligomers in PPS products.

Analysis of Desalination and Purification Process of Polyphenylene Sulfide PPS Resin
Polyphenylene sulfide is usually produced using sodium sulfide and p-dichlorobenzene as raw materials. The polymerization reaction is completed at high temperature (usually around 300°C) and high pressure, and then the finished product of polyphenylene sulfide is obtained after purification and drying. Due to the direct production of polyphenylene sulfide Ether contains a large amount of inorganic ionic impurities, organic impurities and oligomers, which will affect the performance of subsequent polyphenylene sulfide, so it must be purified effectively.


(1) Acid-base neutralization
Cool the product polyphenylene sulfide generated after the polymerization reaction to 100°C~120°C, add acid, control the pH at 3~4, and react for 25~35 minutes at a stirring speed of 20~30 rpm;
(2) Solid-liquid separation
cooling the reaction product obtained in step (1) to 75° C. to 85° C., and separating solid and liquid through a centrifuge to obtain polyphenylene sulfide solid;
(3) Solvent washing
Add an organic solvent to the obtained polyphenylene sulfide solid, control the temperature at 95°C to 105°C, and wash under stirring for 10 to 20 minutes;
(4) steam distillation and washing
The polyphenylene sulfide obtained after washing step (3) is subjected to steam distillation under negative pressure conditions, and the organic solvent remaining in the polyphenylene sulfide solid particles is recovered during the distillation process; after a period of distillation, sampling is carried out. , when the organic solvent content is less than 1%, wash polyphenylene sulfide with steam condensed water at 75°C~85°C;
(5) Dry packaging: the qualified polyphenylene sulfide obtained in step (4) is separated, dried and packaged.



In view of the technical requirements of the existing polyphenylene sulfide PPS resin desalination and purification technology, the filter washing and drying machine (patent number: ZL202022906527.4) developed by Wuxi ZhangHua is aimed at the simultaneous salt-water-containing polymer system in the polymer post-treatment process. The characteristics of the solvent have the advantages of efficient desolventization, dewatering and desalting, reduce the residual content of inorganic salts in the polymer, reduce the chance of product contamination, achieve the purpose of purification, and obtain high-quality, high-performance polyphenylene sulfide resin , to provide feasible post-processing desalination purification equipment for the industrial production of high-quality polyphenylene sulfide.



Polyphenylene sulfide PPS resin desalination purification filtration washing dryer working principle
The cone or barrel of the filter washing and drying machine is equipped with a multi-layer orifice plate and a filter medium superimposed to form a filter device. There is a stirring shaft and a variable-angle variable-lead screw stirring device inside to stir and lift the material during filtration. And scraping operation, the filter cake is automatically pushed out when unloading.

This machine can carry out vacuum filtration or pressure filtration. During the filtration process, the scraper in the machine continuously scrapes the filter cake on the filter screen, so that the material is filtered under the condition of a thin layer of filter cake, and the filtration rate is very high.

If the material needs to be washed, the slurry can be filtered and dried in the machine first, then add the washing liquid, and use the scraper, agitator and extrusion screw in the machine to re-slurry the filter cake, and then pressurize or The slurry is filtered into a filter cake by vacuuming.

In this way, re-slurry filtration is repeated many times to wash the materials thoroughly, and finally all the filter cakes are discharged out of the machine and enter the boiling dryer to complete low-temperature dry explosion.


(1) Pressure filtration or vacuum filtration
Put the solid-liquid mixture produced by the upstream reactor or crystallization equipment into the tank of the two-in-one equipment, open the lower filtrate outlet, pass compressed air or ammonia gas into the equipment, and pressurize and filter the reacted solid-liquid mixture , until the material in the machine is pressed dry. Vacuum can also be drawn at the outlet of the filtrate to vacuum filter the material until the filtrate is drained.

When filtering, the hollow shaft and the hollow screw belt can be rotated clockwise (viewed from the top) to lift the material, and the hollow screw belt can limit the thickness of the filter cake layer when rotating, so that the material is in a thin filter cake Filter under layer conditions to increase the filtration rate. For dry and easy-to-filter materials, it is not necessary to stir when filtering, and the materials are directly filtered to dryness.
(2) Can be washed and filtered multiple times
After some materials are filtered, they need to be washed several times.

After the material is dried in the machine, the washing liquid can be added to the washing liquid inlet on the top, and then the filter cake is evenly repulped through the stirring of the hollow shaft and the hollow ribbon, and the material is pressed dry after the repulping is evenly stirred. If washing once is not enough, it can be washed multiple times, and the above steps can be repeated many times. The operation is convenient and the labor intensity is extremely low.
Washing materials with the above method is called intermittent washing method. Since the materials are pressed dry each time and washing liquid is added for washing, although the valves are opened and closed a little more times during operation, less washing liquid is used.

The machine can also continuously wash the materials, that is, continuously press the washing liquid with a pump or other methods, and use the pressure of the washing liquid to filter, while the hollow shaft and the hollow ribbon are continuously stirred, and the filtrate is continuously discharged from the filtrate outlet until Until the washing requirements are met, the filter cake is finally pressed dry.
(3) Washing liquid collection and reuse system

The all-in-one filter, washing and drying machine adopts a segmented design. Through valve control, multi-stage independent filtration and segmental backflushing can be realized. The filtered washing liquid is discharged from the main pipe, and then flows into the temporary storage tank after being pretreated by the double filter bag filter. . The high-pressure pump at the bottom of the temporary storage tank performs secondary treatment on the precision filter conveyed by the washing liquid, and then uses the valve to control two outputs; one line goes to the washing liquid inlet on the top of the three-in-one, and performs preliminary washing and purification (reuse) of the material; All the way is connected to the washing liquid external treatment pipeline and enters the waste liquid disposal process.

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